1DRBD.CONF(5)                  Configuration Files                 DRBD.CONF(5)
2
3
4

NAME

6       drbd.conf - Configuration file for DRBD's devices
7

INTRODUCTION

9       The file /etc/drbd.conf is read by drbdadm.
10
11       The file format was designed as to allow to have a verbatim copy of the
12       file on both nodes of the cluster. It is highly recommended to do so in
13       order to keep your configuration manageable. The file /etc/drbd.conf
14       should be the same on both nodes of the cluster. Changes to
15       /etc/drbd.conf do not apply immediately.
16
17       By convention the main config contains two include statements. The
18       first one includes the file /etc/drbd.d/global_common.conf, the second
19       one all file with a .res suffix.
20
21           resource r0 {
22                net {
23                     protocol C;
24                     cram-hmac-alg sha1;
25                     shared-secret "FooFunFactory";
26                }
27                disk {
28                     resync-rate 10M;
29                }
30                on alice {
31                     volume 0 {
32                          device    minor 1;
33                          disk      /dev/sda7;
34                          meta-disk internal;
35                     }
36                     address   10.1.1.31:7789;
37                }
38                on bob {
39                     volume 0 {
40                          device    minor 1;
41                          disk      /dev/sda7;
42                          meta-disk internal;
43                     }
44                     address   10.1.1.32:7789;
45                }
46           }
47
48       In this example, there is a single DRBD resource (called r0) which uses
49       protocol C for the connection between its devices. It contains a single
50       volume which runs on host alice uses /dev/drbd1 as devices for its
51       application, and /dev/sda7 as low-level storage for the data. The IP
52       addresses are used to specify the networking interfaces to be used. An
53       eventually running resync process should use about 10MByte/second of IO
54       bandwidth. This resync-rate statement is valid for volume 0, but would
55       also be valid for further volumes. In this example it assigns full
56       10MByte/second to each volume.
57
58       There may be multiple resource sections in a single drbd.conf file. For
59       more examples, please have a look at the DRBD User's Guide[1].
60

FILE FORMAT

62       The file consists of sections and parameters. A section begins with a
63       keyword, sometimes an additional name, and an opening brace (“{”). A
64       section ends with a closing brace (“}”. The braces enclose the
65       parameters.
66
67       section [name] { parameter value; [...] }
68
69       A parameter starts with the identifier of the parameter followed by
70       whitespace. Every subsequent character is considered as part of the
71       parameter's value. A special case are Boolean parameters which consist
72       only of the identifier. Parameters are terminated by a semicolon (“;”).
73
74       Some parameter values have default units which might be overruled by K,
75       M or G. These units are defined in the usual way (K = 2^10 = 1024, M =
76       1024 K, G = 1024 M).
77
78       Comments may be placed into the configuration file and must begin with
79       a hash sign (“#”). Subsequent characters are ignored until the end of
80       the line.
81
82   Sections
83       skip
84
85           Comments out chunks of text, even spanning more than one line.
86           Characters between the keyword skip and the opening brace (“{”) are
87           ignored. Everything enclosed by the braces is skipped. This comes
88           in handy, if you just want to comment out some 'resource [name]
89           {...}' section: just precede it with 'skip'.
90
91       global
92
93           Configures some global parameters. Currently only minor-count,
94           dialog-refresh, disable-ip-verification and usage-count are allowed
95           here. You may only have one global section, preferably as the first
96           section.
97
98       common
99
100           All resources inherit the options set in this section. The common
101           section might have a startup, a options, a handlers, a net and a
102           disk section.
103
104       resource name
105
106           Configures a DRBD resource. Each resource section needs to have two
107           (or more) on host sections and may have a startup, a options, a
108           handlers, a net and a disk section. It might contain volumes
109           sections.
110
111       on host-name
112
113           Carries the necessary configuration parameters for a DRBD device of
114           the enclosing resource.  host-name is mandatory and must match the
115           Linux host name (uname -n) of one of the nodes. You may list more
116           than one host name here, in case you want to use the same
117           parameters on several hosts (you'd have to move the IP around
118           usually). Or you may list more than two such sections.
119
120                    resource r1 {
121                         protocol C;
122                         device minor 1;
123                         meta-disk internal;
124
125                         on alice bob {
126                              address 10.2.2.100:7801;
127                              disk /dev/mapper/some-san;
128                         }
129                         on charlie {
130                              address 10.2.2.101:7801;
131                              disk /dev/mapper/other-san;
132                         }
133                         on daisy {
134                              address 10.2.2.103:7801;
135                              disk /dev/mapper/other-san-as-seen-from-daisy;
136                         }
137                    }
138
139
140           See also the floating section keyword. Required statements in this
141           section: address and volume. Note for backward compatibility and
142           convenience it is valid to embed the statements of a single volume
143           directly into the host section.
144
145       volume vnr
146
147           Defines a volume within a connection. The minor numbers of a
148           replicated volume might be different on different hosts, the volume
149           number (vnr) is what groups them together. Required parameters in
150           this section: device, disk, meta-disk.
151
152       stacked-on-top-of resource
153
154           For a stacked DRBD setup (3 or 4 nodes), a stacked-on-top-of is
155           used instead of an on section. Required parameters in this section:
156           device and address.
157
158       floating AF addr:port
159
160           Carries the necessary configuration parameters for a DRBD device of
161           the enclosing resource. This section is very similar to the on
162           section. The difference to the on section is that the matching of
163           the host sections to machines is done by the IP-address instead of
164           the node name. Required parameters in this section: device, disk,
165           meta-disk, all of which may be inherited from the resource section,
166           in which case you may shorten this section down to just the address
167           identifier.
168
169                    resource r2 {
170                         protocol C;
171                         device minor 2;
172                         disk      /dev/sda7;
173                         meta-disk internal;
174
175                         # short form, device, disk and meta-disk inherited
176                         floating 10.1.1.31:7802;
177
178                         # longer form, only device inherited
179                         floating 10.1.1.32:7802 {
180                              disk /dev/sdb;
181                              meta-disk /dev/sdc8;
182                         }
183                    }
184
185
186       disk
187
188           This section is used to fine tune DRBD's properties in respect to
189           the low level storage. Please refer to drbdsetup(8) for detailed
190           description of the parameters. Optional parameters: on-io-error,
191           size, fencing, disk-barrier, disk-flushes, disk-drain, md-flushes,
192           max-bio-bvecs, resync-rate, resync-after, al-extents, al-updates,
193           c-plan-ahead, c-fill-target, c-delay-target, c-max-rate,
194           c-min-rate, disk-timeout, discard-zeroes-if-aligned,
195           rs-discard-granularity, read-balancing.
196
197       net
198
199           This section is used to fine tune DRBD's properties. Please refer
200           to drbdsetup(8) for a detailed description of this section's
201           parameters. Optional parameters: protocol, sndbuf-size,
202           rcvbuf-size, timeout, connect-int, ping-int, ping-timeout,
203           max-buffers, max-epoch-size, ko-count, allow-two-primaries,
204           cram-hmac-alg, shared-secret, after-sb-0pri, after-sb-1pri,
205           after-sb-2pri, data-integrity-alg, no-tcp-cork, on-congestion,
206           congestion-fill, congestion-extents, verify-alg, use-rle,
207           csums-alg, socket-check-timeout.
208
209       startup
210
211           This section is used to fine tune DRBD's properties. Please refer
212           to drbdsetup(8) for a detailed description of this section's
213           parameters. Optional parameters: wfc-timeout, degr-wfc-timeout,
214           outdated-wfc-timeout, wait-after-sb, stacked-timeouts and
215           become-primary-on.
216
217       options
218
219           This section is used to fine tune the behaviour of the resource
220           object. Please refer to drbdsetup(8) for a detailed description of
221           this section's parameters. Optional parameters: cpu-mask, and
222           on-no-data-accessible.
223
224       handlers
225
226           In this section you can define handlers (executables) that are
227           started by the DRBD system in response to certain events. Optional
228           parameters: pri-on-incon-degr, pri-lost-after-sb, pri-lost,
229           fence-peer (formerly oudate-peer), local-io-error,
230           initial-split-brain, split-brain, before-resync-target,
231           after-resync-target.
232
233           The interface is done via environment variables:
234
235           ·   DRBD_RESOURCE is the name of the resource
236
237           ·   DRBD_MINOR is the minor number of the DRBD device, in decimal.
238
239           ·   DRBD_CONF is the path to the primary configuration file; if you
240               split your configuration into multiple files (e.g. in
241               /etc/drbd.conf.d/), this will not be helpful.
242
243           ·   DRBD_PEER_AF , DRBD_PEER_ADDRESS , DRBD_PEERS are the address
244               family (e.g.  ipv6), the peer's address and hostnames.
245
246
247           DRBD_PEER is deprecated.
248
249           Please note that not all of these might be set for all handlers,
250           and that some values might not be useable for a floating
251           definition.
252
253   Parameters
254       minor-count count
255           count may be a number from 1 to 1048575.
256
257           Minor-count is a sizing hint for DRBD. It helps to right-size
258           various memory pools. It should be set in the in the same order of
259           magnitude than the actual number of minors you use. Per default the
260           module loads with 11 more resources than you have currently in your
261           config but at least 32.
262
263       dialog-refresh time
264           time may be 0 or a positive number.
265
266           The user dialog redraws the second count every time seconds (or
267           does no redraws if time is 0). The default value is 1.
268
269       disable-ip-verification
270           Use disable-ip-verification if, for some obscure reasons, drbdadm
271           can/might not use ip or ifconfig to do a sanity check for the IP
272           address. You can disable the IP verification with this option.
273
274       udev-always-use-vnr
275           When udev asks drbdadm for a list of device related symlinks,
276           drbdadm would suggest symlinks with differing naming conventions,
277           depending on whether the resource has explicit volume VNR { }
278           definitions, or only one single volume with the implicit volume
279           number 0:
280
281               # implicit single volume without "volume 0 {}" block
282               DEVICE=drbd<minor>
283               SYMLINK_BY_RES=drbd/by-res/<resource-name>
284
285               # explicit volume definition: volume VNR { }
286               DEVICE=drbd<minor>
287               SYMLINK_BY_RES=drbd/by-res/<resource-name>/VNR
288
289           If you define this parameter in the global section, drbdadm will
290           always add the .../VNR part, and will not care for whether the
291           volume definition was implicit or explicit.
292
293           For legacy backward compatibility, this is off by default, but we
294           do recommend to enable it.
295
296       usage-count val
297           Please participate in DRBD's online usage counter[2]. The most
298           convenient way to do so is to set this option to yes. Valid options
299           are: yes, no and ask.
300
301       protocol prot-id
302           On the TCP/IP link the specified protocol is used. Valid protocol
303           specifiers are A, B, and C.
304
305           Protocol A: write IO is reported as completed, if it has reached
306           local disk and local TCP send buffer.
307
308           Protocol B: write IO is reported as completed, if it has reached
309           local disk and remote buffer cache.
310
311           Protocol C: write IO is reported as completed, if it has reached
312           both local and remote disk.
313
314       device name minor nr
315
316           The name of the block device node of the resource being described.
317           You must use this device with your application (file system) and
318           you must not use the low level block device which is specified with
319           the disk parameter.
320
321           One can ether omit the name or minor and the minor number. If you
322           omit the name a default of /dev/drbdminor will be used.
323
324           Udev will create additional symlinks in /dev/drbd/by-res and
325           /dev/drbd/by-disk.
326
327       disk name
328
329           DRBD uses this block device to actually store and retrieve the
330           data. Never access such a device while DRBD is running on top of
331           it. This also holds true for dumpe2fs(8) and similar commands.
332
333       address AF addr:port
334
335           A resource needs one IP address per device, which is used to wait
336           for incoming connections from the partner device respectively to
337           reach the partner device.  AF must be one of ipv4, ipv6, ssocks or
338           sdp (for compatibility reasons sci is an alias for ssocks). It may
339           be omited for IPv4 addresses. The actual IPv6 address that follows
340           the ipv6 keyword must be placed inside brackets: ipv6
341           [fd01:2345:6789:abcd::1]:7800.
342
343           Each DRBD resource needs a TCP port which is used to connect to the
344           node's partner device. Two different DRBD resources may not use the
345           same addr:port combination on the same node.
346
347       meta-disk internal,
348       meta-disk device,
349       meta-disk device [index]
350
351           Internal means that the last part of the backing device is used to
352           store the meta-data. The size of the meta-data is computed based on
353           the size of the device.
354
355           When a device is specified, either with or without an index, DRBD
356           stores the meta-data on this device. Without index, the size of the
357           meta-data is determined by the size of the data device. This is
358           usually used with LVM, which allows to have many variable sized
359           block devices. The meta-data size is 36kB + Backing-Storage-size /
360           32k, rounded up to the next 4kb boundary. (Rule of the thumb:
361           32kByte per 1GByte of storage, rounded up to the next MB.)
362
363           When an index is specified, each index number refers to a fixed
364           slot of meta-data of 128 MB, which allows a maximum data size of 4
365           TiB. This way, multiple DBRD devices can share the same meta-data
366           device. For example, if /dev/sde6[0] and /dev/sde6[1] are used,
367           /dev/sde6 must be at least 256 MB big. Because of the hard size
368           limit, use of meta-disk indexes is discouraged.
369
370       on-io-error handler
371           handler is taken, if the lower level device reports io-errors to
372           the upper layers.
373
374           handler may be pass_on, call-local-io-error or detach.
375
376           pass_on: The node downgrades the disk status to inconsistent, marks
377           the erroneous block as inconsistent in the bitmap and retries the
378           IO on the remote node.
379
380           call-local-io-error: Call the handler script local-io-error.
381
382           detach: The node drops its low level device, and continues in
383           diskless mode.
384
385       fencing fencing_policy
386
387           By fencing we understand preventive measures to avoid situations
388           where both nodes are primary and disconnected (AKA split brain).
389
390           Valid fencing policies are:
391
392           dont-care
393               This is the default policy. No fencing actions are taken.
394
395           resource-only
396               If a node becomes a disconnected primary, it tries to fence the
397               peer's disk. This is done by calling the fence-peer handler.
398               The handler is supposed to reach the other node over
399               alternative communication paths and call 'drbdadm outdate res'
400               there.
401
402           resource-and-stonith
403               If a node becomes a disconnected primary, it freezes all its IO
404               operations and calls its fence-peer handler. The fence-peer
405               handler is supposed to reach the peer over alternative
406               communication paths and call 'drbdadm outdate res' there. In
407               case it cannot reach the peer it should stonith the peer. IO is
408               resumed as soon as the situation is resolved. In case your
409               handler fails, you can resume IO with the resume-io command.
410
411       disk-barrier,
412       disk-flushes,
413       disk-drain
414           DRBD has four implementations to express write-after-write
415           dependencies to its backing storage device. DRBD will use the first
416           method that is supported by the backing storage device and that is
417           not disabled. By default the flush method is used.
418
419           Since drbd-8.4.2 disk-barrier is disabled by default because since
420           linux-2.6.36 (or 2.6.32 RHEL6) there is no reliable way to
421           determine if queuing of IO-barriers works.  Dangerous only enable
422           if you are told so by one that knows for sure.
423
424           When selecting the method you should not only base your decision on
425           the measurable performance. In case your backing storage device has
426           a volatile write cache (plain disks, RAID of plain disks) you
427           should use one of the first two. In case your backing storage
428           device has battery-backed write cache you may go with option 3.
429           Option 4 (disable everything, use "none") is dangerous on most IO
430           stacks, may result in write-reordering, and if so, can
431           theoretically be the reason for data corruption, or disturb the
432           DRBD protocol, causing spurious disconnect/reconnect cycles.  Do
433           not use no-disk-drain.
434
435           Unfortunately device mapper (LVM) might not support barriers.
436
437           The letter after "wo:" in /proc/drbd indicates with method is
438           currently in use for a device: b, f, d, n. The implementations are:
439
440           barrier
441               The first requires that the driver of the backing storage
442               device support barriers (called 'tagged command queuing' in
443               SCSI and 'native command queuing' in SATA speak). The use of
444               this method can be enabled by setting the disk-barrier options
445               to yes.
446
447           flush
448               The second requires that the backing device support disk
449               flushes (called 'force unit access' in the drive vendors
450               speak). The use of this method can be disabled setting
451               disk-flushes to no.
452
453           drain
454               The third method is simply to let write requests drain before
455               write requests of a new reordering domain are issued. This was
456               the only implementation before 8.0.9.
457
458           none
459               The fourth method is to not express write-after-write
460               dependencies to the backing store at all, by also specifying
461               no-disk-drain. This is dangerous on most IO stacks, may result
462               in write-reordering, and if so, can theoretically be the reason
463               for data corruption, or disturb the DRBD protocol, causing
464               spurious disconnect/reconnect cycles.  Do not use
465               no-disk-drain.
466
467       md-flushes
468           Disables the use of disk flushes and barrier BIOs when accessing
469           the meta data device. See the notes on disk-flushes.
470
471       max-bio-bvecs
472           In some special circumstances the device mapper stack manages to
473           pass BIOs to DRBD that violate the constraints that are set forth
474           by DRBD's merge_bvec() function and which have more than one bvec.
475           A known example is: phys-disk -> DRBD -> LVM -> Xen -> misaligned
476           partition (63) -> DomU FS. Then you might see "bio would need to,
477           but cannot, be split:" in the Dom0's kernel log.
478
479           The best workaround is to proper align the partition within the VM
480           (E.g. start it at sector 1024). This costs 480 KiB of storage.
481           Unfortunately the default of most Linux partitioning tools is to
482           start the first partition at an odd number (63). Therefore most
483           distribution's install helpers for virtual linux machines will end
484           up with misaligned partitions. The second best workaround is to
485           limit DRBD's max bvecs per BIO (= max-bio-bvecs) to 1, but that
486           might cost performance.
487
488           The default value of max-bio-bvecs is 0, which means that there is
489           no user imposed limitation.
490
491       disk-timeout
492           If the lower-level device on which a DRBD device stores its data
493           does not finish an I/O request within the defined disk-timeout,
494           DRBD treats this as a failure. The lower-level device is detached,
495           and the device's disk state advances to Diskless. If DRBD is
496           connected to one or more peers, the failed request is passed on to
497           one of them.
498
499           This option is dangerous and may lead to kernel panic!
500
501           "Aborting" requests, or force-detaching the disk, is intended for
502           completely blocked/hung local backing devices which do no longer
503           complete requests at all, not even do error completions. In this
504           situation, usually a hard-reset and failover is the only way out.
505
506           By "aborting", basically faking a local error-completion, we allow
507           for a more graceful swichover by cleanly migrating services. Still
508           the affected node has to be rebooted "soon".
509
510           By completing these requests, we allow the upper layers to re-use
511           the associated data pages.
512
513           If later the local backing device "recovers", and now DMAs some
514           data from disk into the original request pages, in the best case it
515           will just put random data into unused pages; but typically it will
516           corrupt meanwhile completely unrelated data, causing all sorts of
517           damage.
518
519           Which means delayed successful completion, especially for READ
520           requests, is a reason to panic(). We assume that a delayed *error*
521           completion is OK, though we still will complain noisily about it.
522
523           The default value of disk-timeout is 0, which stands for an
524           infinite timeout. Timeouts are specified in units of 0.1 seconds.
525           This option is available since DRBD 8.3.12.
526
527       discard-zeroes-if-aligned {yes | no}
528
529           There are several aspects to discard/trim/unmap support on linux
530           block devices. Even if discard is supported in general, it may fail
531           silently, or may partially ignore discard requests. Devices also
532           announce whether reading from unmapped blocks returns defined data
533           (usually zeroes), or undefined data (possibly old data, possibly
534           garbage).
535
536           If on different nodes, DRBD is backed by devices with differing
537           discard characteristics, discards may lead to data divergence (old
538           data or garbage left over on one backend, zeroes due to unmapped
539           areas on the other backend). Online verify would now potentially
540           report tons of spurious differences. While probably harmless for
541           most use cases (fstrim on a file system), DRBD cannot have that.
542
543           To play safe, we have to disable discard support, if our local
544           backend (on a Primary) does not support "discard_zeroes_data=true".
545           We also have to translate discards to explicit zero-out on the
546           receiving side, unless the receiving side (Secondary) supports
547           "discard_zeroes_data=true", thereby allocating areas what were
548           supposed to be unmapped.
549
550           There are some devices (notably the LVM/DM thin provisioning) that
551           are capable of discard, but announce discard_zeroes_data=false. In
552           the case of DM-thin, discards aligned to the chunk size will be
553           unmapped, and reading from unmapped sectors will return zeroes.
554           However, unaligned partial head or tail areas of discard requests
555           will be silently ignored.
556
557           If we now add a helper to explicitly zero-out these unaligned
558           partial areas, while passing on the discard of the aligned full
559           chunks, we effectively achieve discard_zeroes_data=true on such
560           devices.
561
562           Setting discard-zeroes-if-aligned to yes will allow DRBD to use
563           discards, and to announce discard_zeroes_data=true, even on
564           backends that announce discard_zeroes_data=false.
565
566           Setting discard-zeroes-if-aligned to no will cause DRBD to always
567           fall-back to zero-out on the receiving side, and to not even
568           announce discard capabilities on the Primary, if the respective
569           backend announces discard_zeroes_data=false.
570
571           We used to ignore the discard_zeroes_data setting completely. To
572           not break established and expected behaviour, and suddenly cause
573           fstrim on thin-provisioned LVs to run out-of-space instead of
574           freeing up space, the default value is yes.
575
576           This option is available since 8.4.7.
577
578       read-balancing method
579           The supported methods for load balancing of read requests are
580           prefer-local, prefer-remote, round-robin, least-pending,
581           when-congested-remote, 32K-striping, 64K-striping, 128K-striping,
582           256K-striping, 512K-striping and 1M-striping.
583
584           The default value of is prefer-local. This option is available
585           since 8.4.1.
586
587       rs-discard-granularity byte
588           When rs-discard-granularity is set to a non zero, positive value
589           then DRBD tries to do a resync operation in requests of this size.
590           In case such a block contains only zero bytes on the sync source
591           node, the sync target node will issue a discard/trim/unmap command
592           for the area.
593
594           The value is constrained by the discard granularity of the backing
595           block device. In case rs-discard-granularity is not a multiplier of
596           the discard granularity of the backing block device DRBD rounds it
597           up. The feature only gets active if the backing block device reads
598           back zeroes after a discard command.
599
600           The default value of is 0. This option is available since 8.4.7.
601
602       sndbuf-size size
603           size is the size of the TCP socket send buffer. The default value
604           is 0, i.e. autotune. You can specify smaller or larger values.
605           Larger values are appropriate for reasonable write throughput with
606           protocol A over high latency networks. Values below 32K do not make
607           sense. Since 8.0.13 resp. 8.2.7, setting the size value to 0 means
608           that the kernel should autotune this.
609
610       rcvbuf-size size
611           size is the size of the TCP socket receive buffer. The default
612           value is 0, i.e. autotune. You can specify smaller or larger
613           values. Usually this should be left at its default. Setting the
614           size value to 0 means that the kernel should autotune this.
615
616       timeout time
617
618           If the partner node fails to send an expected response packet
619           within time tenths of a second, the partner node is considered dead
620           and therefore the TCP/IP connection is abandoned. This must be
621           lower than connect-int and ping-int. The default value is 60 = 6
622           seconds, the unit 0.1 seconds.
623
624       connect-int time
625
626           In case it is not possible to connect to the remote DRBD device
627           immediately, DRBD keeps on trying to connect. With this option you
628           can set the time between two retries. The default value is 10
629           seconds, the unit is 1 second.
630
631       ping-int time
632
633           If the TCP/IP connection linking a DRBD device pair is idle for
634           more than time seconds, DRBD will generate a keep-alive packet to
635           check if its partner is still alive. The default is 10 seconds, the
636           unit is 1 second.
637
638       ping-timeout time
639
640           The time the peer has time to answer to a keep-alive packet. In
641           case the peer's reply is not received within this time period, it
642           is considered as dead. The default value is 500ms, the default unit
643           are tenths of a second.
644
645       max-buffers number
646
647           Limits the memory usage per DRBD minor device on the receiving
648           side, or for internal buffers during resync or online-verify. Unit
649           is PAGE_SIZE, which is 4 KiB on most systems. The minimum possible
650           setting is hard coded to 32 (=128 KiB). These buffers are used to
651           hold data blocks while they are written to/read from disk. To avoid
652           possible distributed deadlocks on congestion, this setting is used
653           as a throttle threshold rather than a hard limit. Once more than
654           max-buffers pages are in use, further allocation from this pool is
655           throttled. You want to increase max-buffers if you cannot saturate
656           the IO backend on the receiving side.
657
658       ko-count number
659
660           In case the secondary node fails to complete a single write request
661           for count times the timeout, it is expelled from the cluster. (I.e.
662           the primary node will kill and restart the connection.) To disable
663           this feature, you should explicitly set it to 0; defaults may
664           change between versions.
665
666       max-epoch-size number
667
668           The highest number of data blocks between two write barriers. If
669           you set this smaller than 10, you might decrease your performance.
670
671       allow-two-primaries
672
673           With this option set you may assign the primary role to both nodes.
674           You only should use this option if you use a shared storage file
675           system on top of DRBD. At the time of writing the only ones are:
676           OCFS2 and GFS. If you use this option with any other file system,
677           you are going to crash your nodes and to corrupt your data!
678
679       unplug-watermark number
680           This setting has no effect with recent kernels that use explicit
681           on-stack plugging (upstream Linux kernel 2.6.39, distributions may
682           have backported).
683
684           When the number of pending write requests on the standby
685           (secondary) node exceeds the unplug-watermark, we trigger the
686           request processing of our backing storage device. Some storage
687           controllers deliver better performance with small values, others
688           deliver best performance when the value is set to the same value as
689           max-buffers, yet others don't feel much effect at all. Minimum 16,
690           default 128, maximum 131072.
691
692       cram-hmac-alg
693
694           You need to specify the HMAC algorithm to enable peer
695           authentication at all. You are strongly encouraged to use peer
696           authentication. The HMAC algorithm will be used for the challenge
697           response authentication of the peer. You may specify any digest
698           algorithm that is named in /proc/crypto.
699
700       shared-secret
701
702           The shared secret used in peer authentication. May be up to 64
703           characters. Note that peer authentication is disabled as long as no
704           cram-hmac-alg (see above) is specified.
705
706       after-sb-0pri  policy
707           possible policies are:
708
709           disconnect
710               No automatic resynchronization, simply disconnect.
711
712           discard-younger-primary
713               Auto sync from the node that was primary before the split-brain
714               situation happened.
715
716           discard-older-primary
717               Auto sync from the node that became primary as second during
718               the split-brain situation.
719
720           discard-zero-changes
721               In case one node did not write anything since the split brain
722               became evident, sync from the node that wrote something to the
723               node that did not write anything. In case none wrote anything
724               this policy uses a random decision to perform a "resync" of 0
725               blocks. In case both have written something this policy
726               disconnects the nodes.
727
728           discard-least-changes
729               Auto sync from the node that touched more blocks during the
730               split brain situation.
731
732           discard-node-NODENAME
733               Auto sync to the named node.
734
735       after-sb-1pri  policy
736           possible policies are:
737
738           disconnect
739               No automatic resynchronization, simply disconnect.
740
741           consensus
742               Discard the version of the secondary if the outcome of the
743               after-sb-0pri algorithm would also destroy the current
744               secondary's data. Otherwise disconnect.
745
746           violently-as0p
747               Always take the decision of the after-sb-0pri algorithm, even
748               if that causes an erratic change of the primary's view of the
749               data. This is only useful if you use a one-node FS (i.e. not
750               OCFS2 or GFS) with the allow-two-primaries flag, AND if you
751               really know what you are doing. This is DANGEROUS and MAY CRASH
752               YOUR MACHINE if you have an FS mounted on the primary node.
753
754           discard-secondary
755               Discard the secondary's version.
756
757           call-pri-lost-after-sb
758               Always honor the outcome of the after-sb-0pri algorithm. In
759               case it decides the current secondary has the right data, it
760               calls the "pri-lost-after-sb" handler on the current primary.
761
762       after-sb-2pri  policy
763           possible policies are:
764
765           disconnect
766               No automatic resynchronization, simply disconnect.
767
768           violently-as0p
769               Always take the decision of the after-sb-0pri algorithm, even
770               if that causes an erratic change of the primary's view of the
771               data. This is only useful if you use a one-node FS (i.e. not
772               OCFS2 or GFS) with the allow-two-primaries flag, AND if you
773               really know what you are doing. This is DANGEROUS and MAY CRASH
774               YOUR MACHINE if you have an FS mounted on the primary node.
775
776           call-pri-lost-after-sb
777               Call the "pri-lost-after-sb" helper program on one of the
778               machines. This program is expected to reboot the machine, i.e.
779               make it secondary.
780
781       always-asbp
782           Normally the automatic after-split-brain policies are only used if
783           current states of the UUIDs do not indicate the presence of a third
784           node.
785
786           With this option you request that the automatic after-split-brain
787           policies are used as long as the data sets of the nodes are somehow
788           related. This might cause a full sync, if the UUIDs indicate the
789           presence of a third node. (Or double faults led to strange UUID
790           sets.)
791
792       rr-conflict  policy
793           This option helps to solve the cases when the outcome of the resync
794           decision is incompatible with the current role assignment in the
795           cluster.
796
797           disconnect
798               No automatic resynchronization, simply disconnect.
799
800           violently
801               Sync to the primary node is allowed, violating the assumption
802               that data on a block device are stable for one of the nodes.
803               Dangerous, do not use.
804
805           call-pri-lost
806               Call the pri-lost-after-sb helper program on one of the
807               machines unless that machine can demote to secondary. The
808               helper program is expected to reboot the machine, which brings
809               the node into a secondary role. Which machine runs the helper
810               program is determined by the after-sb-0pri strategy.
811
812       data-integrity-alg  alg
813           DRBD can ensure the data integrity of the user's data on the
814           network by comparing hash values. Normally this is ensured by the
815           16 bit checksums in the headers of TCP/IP packets.
816
817           This option can be set to any of the kernel's data digest
818           algorithms. In a typical kernel configuration you should have at
819           least one of md5, sha1, and crc32c available. By default this is
820           not enabled.
821
822           See also the notes on data integrity.
823
824       tcp-cork
825           DRBD usually uses the TCP socket option TCP_CORK to hint to the
826           network stack when it can expect more data, and when it should
827           flush out what it has in its send queue. It turned out that there
828           is at least one network stack that performs worse when one uses
829           this hinting method. Therefore we introducted this option. By
830           setting tcp-cork to no you can disable the setting and clearing of
831           the TCP_CORK socket option by DRBD.
832
833       on-congestion congestion_policy,
834       congestion-fill fill_threshold,
835       congestion-extents active_extents_threshold
836           By default DRBD blocks when the available TCP send queue becomes
837           full. That means it will slow down the application that generates
838           the write requests that cause DRBD to send more data down that TCP
839           connection.
840
841           When DRBD is deployed with DRBD-proxy it might be more desirable
842           that DRBD goes into AHEAD/BEHIND mode shortly before the send queue
843           becomes full. In AHEAD/BEHIND mode DRBD does no longer replicate
844           data, but still keeps the connection open.
845
846           The advantage of the AHEAD/BEHIND mode is that the application is
847           not slowed down, even if DRBD-proxy's buffer is not sufficient to
848           buffer all write requests. The downside is that the peer node falls
849           behind, and that a resync will be necessary to bring it back into
850           sync. During that resync the peer node will have an inconsistent
851           disk.
852
853           Available congestion_policys are block and pull-ahead. The default
854           is block.  Fill_threshold might be in the range of 0 to 10GiBytes.
855           The default is 0 which disables the check.
856           Active_extents_threshold has the same limits as al-extents.
857
858           The AHEAD/BEHIND mode and its settings are available since DRBD
859           8.3.10.
860
861       wfc-timeout time
862           Wait for connection timeout.
863
864           The init script drbd(8) blocks the boot process until the DRBD
865           resources are connected. When the cluster manager starts later, it
866           does not see a resource with internal split-brain. In case you want
867           to limit the wait time, do it here. Default is 0, which means
868           unlimited. The unit is seconds.
869
870       degr-wfc-timeout time
871
872           Wait for connection timeout, if this node was a degraded cluster.
873           In case a degraded cluster (= cluster with only one node left) is
874           rebooted, this timeout value is used instead of wfc-timeout,
875           because the peer is less likely to show up in time, if it had been
876           dead before. Value 0 means unlimited.
877
878       outdated-wfc-timeout time
879
880           Wait for connection timeout, if the peer was outdated. In case a
881           degraded cluster (= cluster with only one node left) with an
882           outdated peer disk is rebooted, this timeout value is used instead
883           of wfc-timeout, because the peer is not allowed to become primary
884           in the meantime. Value 0 means unlimited.
885
886       wait-after-sb
887           By setting this option you can make the init script to continue to
888           wait even if the device pair had a split brain situation and
889           therefore refuses to connect.
890
891       become-primary-on node-name
892           Sets on which node the device should be promoted to primary role by
893           the init script. The node-name might either be a host name or the
894           keyword both. When this option is not set the devices stay in
895           secondary role on both nodes. Usually one delegates the role
896           assignment to a cluster manager (e.g. heartbeat).
897
898       stacked-timeouts
899           Usually wfc-timeout and degr-wfc-timeout are ignored for stacked
900           devices, instead twice the amount of connect-int is used for the
901           connection timeouts. With the stacked-timeouts keyword you disable
902           this, and force DRBD to mind the wfc-timeout and degr-wfc-timeout
903           statements. Only do that if the peer of the stacked resource is
904           usually not available or will usually not become primary. By using
905           this option incorrectly, you run the risk of causing unexpected
906           split brain.
907
908       resync-rate rate
909
910           To ensure a smooth operation of the application on top of DRBD, it
911           is possible to limit the bandwidth which may be used by background
912           synchronizations. The default is 250 KB/sec, the default unit is
913           KB/sec. Optional suffixes K, M, G are allowed.
914
915       use-rle
916
917           During resync-handshake, the dirty-bitmaps of the nodes are
918           exchanged and merged (using bit-or), so the nodes will have the
919           same understanding of which blocks are dirty. On large devices, the
920           fine grained dirty-bitmap can become large as well, and the bitmap
921           exchange can take quite some time on low-bandwidth links.
922
923           Because the bitmap typically contains compact areas where all bits
924           are unset (clean) or set (dirty), a simple run-length encoding
925           scheme can considerably reduce the network traffic necessary for
926           the bitmap exchange.
927
928           For backward compatibility reasons, and because on fast links this
929           possibly does not improve transfer time but consumes cpu cycles,
930           this defaults to off.
931
932       socket-check-timeout value
933
934           In setups involving a DRBD-proxy and connections that experience a
935           lot of buffer-bloat it might be necessary to set ping-timeout to an
936           unusual high value. By default DRBD uses the same value to wait if
937           a newly established TCP-connection is stable. Since the DRBD-proxy
938           is usually located in the same data center such a long wait time
939           may hinder DRBD's connect process.
940
941           In such setups socket-check-timeout should be set to at least to
942           the round trip time between DRBD and DRBD-proxy. I.e. in most cases
943           to 1.
944
945           The default unit is tenths of a second, the default value is 0
946           (which causes DRBD to use the value of ping-timeout instead).
947           Introduced in 8.4.5.
948
949       resync-after res-name
950
951           By default, resynchronization of all devices would run in parallel.
952           By defining a resync-after dependency, the resynchronization of
953           this resource will start only if the resource res-name is already
954           in connected state (i.e., has finished its resynchronization).
955
956       al-extents extents
957
958           DRBD automatically performs hot area detection. With this parameter
959           you control how big the hot area (= active set) can get. Each
960           extent marks 4M of the backing storage (= low-level device). In
961           case a primary node leaves the cluster unexpectedly, the areas
962           covered by the active set must be resynced upon rejoining of the
963           failed node. The data structure is stored in the meta-data area,
964           therefore each change of the active set is a write operation to the
965           meta-data device. A higher number of extents gives longer resync
966           times but less updates to the meta-data. The default number of
967           extents is 1237. (Minimum: 7, Maximum: 65534)
968
969           Note that the effective maximum may be smaller, depending on how
970           you created the device meta data, see also drbdmeta(8). The
971           effective maximum is 919 * (available on-disk activity-log
972           ring-buffer area/4kB -1), the default 32kB ring-buffer effects a
973           maximum of 6433 (covers more than 25 GiB of data). We recommend to
974           keep this well within the amount your backend storage and
975           replication link are able to resync inside of about 5 minutes.
976
977       al-updates {yes | no}
978
979           DRBD's activity log transaction writing makes it possible, that
980           after the crash of a primary node a partial (bit-map based) resync
981           is sufficient to bring the node back to up-to-date. Setting
982           al-updates to no might increase normal operation performance but
983           causes DRBD to do a full resync when a crashed primary gets
984           reconnected. The default value is yes.
985
986       verify-alg hash-alg
987           During online verification (as initiated by the verify
988           sub-command), rather than doing a bit-wise comparison, DRBD applies
989           a hash function to the contents of every block being verified, and
990           compares that hash with the peer. This option defines the hash
991           algorithm being used for that purpose. It can be set to any of the
992           kernel's data digest algorithms. In a typical kernel configuration
993           you should have at least one of md5, sha1, and crc32c available. By
994           default this is not enabled; you must set this option explicitly in
995           order to be able to use on-line device verification.
996
997           See also the notes on data integrity.
998
999       csums-alg hash-alg
1000           A resync process sends all marked data blocks from the source to
1001           the destination node, as long as no csums-alg is given. When one is
1002           specified the resync process exchanges hash values of all marked
1003           blocks first, and sends only those data blocks that have different
1004           hash values.
1005
1006           This setting is useful for DRBD setups with low bandwidth links.
1007           During the restart of a crashed primary node, all blocks covered by
1008           the activity log are marked for resync. But a large part of those
1009           will actually be still in sync, therefore using csums-alg will
1010           lower the required bandwidth in exchange for CPU cycles.
1011
1012       c-plan-ahead plan_time,
1013       c-fill-target fill_target,
1014       c-delay-target delay_target,
1015       c-max-rate max_rate
1016           The dynamic resync speed controller gets enabled with setting
1017           plan_time to a positive value. It aims to fill the buffers along
1018           the data path with either a constant amount of data fill_target, or
1019           aims to have a constant delay time of delay_target along the path.
1020           The controller has an upper bound of max_rate.
1021
1022           By plan_time the agility of the controller is configured. Higher
1023           values yield for slower/lower responses of the controller to
1024           deviation from the target value. It should be at least 5 times RTT.
1025           For regular data paths a fill_target in the area of 4k to 100k is
1026           appropriate. For a setup that contains drbd-proxy it is advisable
1027           to use delay_target instead. Only when fill_target is set to 0 the
1028           controller will use delay_target. 5 times RTT is a reasonable
1029           starting value.  Max_rate should be set to the bandwidth available
1030           between the DRBD-hosts and the machines hosting DRBD-proxy, or to
1031           the available disk-bandwidth.
1032
1033           The default value of plan_time is 0, the default unit is 0.1
1034           seconds.  Fill_target has 0 and sectors as default unit.
1035           Delay_target has 1 (100ms) and 0.1 as default unit.  Max_rate has
1036           10240 (100MiB/s) and KiB/s as default unit.
1037
1038           The dynamic resync speed controller and its settings are available
1039           since DRBD 8.3.9.
1040
1041       c-min-rate min_rate
1042           A node that is primary and sync-source has to schedule application
1043           IO requests and resync IO requests. The min_rate tells DRBD use
1044           only up to min_rate for resync IO and to dedicate all other
1045           available IO bandwidth to application requests.
1046
1047           Note: The value 0 has a special meaning. It disables the limitation
1048           of resync IO completely, which might slow down application IO
1049           considerably. Set it to a value of 1, if you prefer that resync IO
1050           never slows down application IO.
1051
1052           Note: Although the name might suggest that it is a lower bound for
1053           the dynamic resync speed controller, it is not. If the DRBD-proxy
1054           buffer is full, the dynamic resync speed controller is free to
1055           lower the resync speed down to 0, completely independent of the
1056           c-min-rate setting.
1057
1058           The default value of min_rate is 250, in units of KiB/s
1059
1060       on-no-data-accessible ond-policy
1061           This setting controls what happens to IO requests on a degraded,
1062           disk less node (I.e. no data store is reachable). The available
1063           policies are io-error and suspend-io.
1064
1065           If ond-policy is set to suspend-io you can either resume IO by
1066           attaching/connecting the last lost data storage, or by the drbdadm
1067           resume-io res command. The latter will result in IO errors of
1068           course.
1069
1070           The default is io-error. This setting is available since DRBD
1071           8.3.9.
1072
1073       cpu-mask cpu-mask
1074
1075           Sets the cpu-affinity-mask for DRBD's kernel threads of this
1076           device. The default value of cpu-mask is 0, which means that DRBD's
1077           kernel threads should be spread over all CPUs of the machine. This
1078           value must be given in hexadecimal notation. If it is too big it
1079           will be truncated.
1080
1081       pri-on-incon-degr cmd
1082
1083           This handler is called if the node is primary, degraded and if the
1084           local copy of the data is inconsistent.
1085
1086       pri-lost-after-sb cmd
1087
1088           The node is currently primary, but lost the after-split-brain auto
1089           recovery procedure. As as consequence, it should be abandoned.
1090
1091       pri-lost cmd
1092
1093           The node is currently primary, but DRBD's algorithm thinks that it
1094           should become sync target. As a consequence it should give up its
1095           primary role.
1096
1097       fence-peer cmd
1098
1099           The handler is part of the fencing mechanism. This handler is
1100           called in case the node needs to fence the peer's disk. It should
1101           use other communication paths than DRBD's network link.
1102
1103       local-io-error cmd
1104
1105           DRBD got an IO error from the local IO subsystem.
1106
1107       initial-split-brain cmd
1108
1109           DRBD has connected and detected a split brain situation. This
1110           handler can alert someone in all cases of split brain, not just
1111           those that go unresolved.
1112
1113       split-brain cmd
1114
1115           DRBD detected a split brain situation but remains unresolved.
1116           Manual recovery is necessary. This handler should alert someone on
1117           duty.
1118
1119       before-resync-target cmd
1120
1121           DRBD calls this handler just before a resync begins on the node
1122           that becomes resync target. It might be used to take a snapshot of
1123           the backing block device.
1124
1125       after-resync-target cmd
1126
1127           DRBD calls this handler just after a resync operation finished on
1128           the node whose disk just became consistent after being inconsistent
1129           for the duration of the resync. It might be used to remove a
1130           snapshot of the backing device that was created by the
1131           before-resync-target handler.
1132
1133   Other Keywords
1134       include file-pattern
1135
1136           Include all files matching the wildcard pattern file-pattern. The
1137           include statement is only allowed on the top level, i.e. it is not
1138           allowed inside any section.
1139

NOTES ON DATA INTEGRITY

1141       There are two independent methods in DRBD to ensure the integrity of
1142       the mirrored data. The online-verify mechanism and the
1143       data-integrity-alg of the network section.
1144
1145       Both mechanisms might deliver false positives if the user of DRBD
1146       modifies the data which gets written to disk while the transfer goes
1147       on. This may happen for swap, or for certain append while global sync,
1148       or truncate/rewrite workloads, and not necessarily poses a problem for
1149       the integrity of the data. Usually when the initiator of the data
1150       transfer does this, it already knows that that data block will not be
1151       part of an on disk data structure, or will be resubmitted with correct
1152       data soon enough.
1153
1154       The data-integrity-alg causes the receiving side to log an error about
1155       "Digest integrity check FAILED: Ns +x\n", where N is the sector offset,
1156       and x is the size of the request in bytes. It will then disconnect, and
1157       reconnect, thus causing a quick resync. If the sending side at the same
1158       time detected a modification, it warns about "Digest mismatch, buffer
1159       modified by upper layers during write: Ns +x\n", which shows that this
1160       was a false positive. The sending side may detect these buffer
1161       modifications immediately after the unmodified data has been copied to
1162       the tcp buffers, in which case the receiving side won't notice it.
1163
1164       The most recent (2007) example of systematic corruption was an issue
1165       with the TCP offloading engine and the driver of a certain type of GBit
1166       NIC. The actual corruption happened on the DMA transfer from core
1167       memory to the card. Since the TCP checksum gets calculated on the card,
1168       this type of corruption stays undetected as long as you do not use
1169       either the online verify or the data-integrity-alg.
1170
1171       We suggest to use the data-integrity-alg only during a pre-production
1172       phase due to its CPU costs. Further we suggest to do online verify runs
1173       regularly e.g. once a month during a low load period.
1174

VERSION

1176       This document was revised for version 8.4.0 of the DRBD distribution.
1177

AUTHOR

1179       Written by Philipp Reisner <philipp.reisner@linbit.com> and Lars
1180       Ellenberg <lars.ellenberg@linbit.com>.
1181

REPORTING BUGS

1183       Report bugs to <drbd-user@lists.linbit.com>.
1184
1186       Copyright 2001-2008 LINBIT Information Technologies, Philipp Reisner,
1187       Lars Ellenberg. This is free software; see the source for copying
1188       conditions. There is NO warranty; not even for MERCHANTABILITY or
1189       FITNESS FOR A PARTICULAR PURPOSE.
1190

SEE ALSO

1192       drbd(8), drbddisk(8), drbdsetup(8), drbdmeta(8), drbdadm(8), DRBD
1193       User's Guide[1], DRBD web site[3]
1194

NOTES

1196        1. DRBD User's Guide
1197           http://www.drbd.org/users-guide/
1198
1199        2. DRBD's online usage counter
1200           http://usage.drbd.org
1201
1202        3. DRBD web site
1203           http://www.drbd.org/
1204
1205
1206
1207DRBD 8.4.0                        6 May 2011                      DRBD.CONF(5)
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