1MDADM.CONF(5) File Formats Manual MDADM.CONF(5)
2
6 mdadm.conf - configuration for management of Software RAID with mdadm
7
9 /etc/mdadm.conf
10
12 mdadm is a tool for creating, managing, and monitoring RAID devices
13 using the md driver in Linux.
14 Some common tasks, such as assembling all arrays, can be simplified by
16 describing the devices and arrays in this configuration file.
17 SYNTAX
20 The file should be seen as a collection of words separated by white
21 space (space, tab, or newline). Any word that beings with a hash sign
22 (#) starts a comment and that word together with the remainder of the
23 line is ignored.
24 Any line that starts with white space (space or tab) is treated as
26 though it were a continuation of the previous line.
27 Empty lines are ignored, but otherwise each (non continuation) line
29 must start with a keyword as listed below. The keywords are case
30 insensitive and can be abbreviated to 3 characters.
31 The keywords are:
33 DEVICE A device line lists the devices (whole devices or partitions)
35 that might contain a component of an MD array. When looking for
36 the components of an array, mdadm will scan these devices (or
37 any devices listed on the command line).
38 The device line may contain a number of different devices (sepa‐
40 rated by spaces) and each device name can contain wild cards as
41 defined by glob(7).
42 Also, there may be several device lines present in the file.
44 Alternatively, a device line can contain either of both of the
46 words containers and partitions. The word containers will cause
47 mdadm to look for assembled CONTAINER arrays and included them
48 as a source for assembling further arrays.
49 The word partitions will cause mdadm to read /proc/partitions
51 and include all devices and partitions found therein. mdadm
52 does not use the names from /proc/partitions but only the major
53 and minor device numbers. It scans /dev to find the name that
54 matches the numbers.
55 If no DEVICE line is present, then "DEVICE partitions contain‐
57 ers" is assumed.
58 For example:
60 DEVICE /dev/hda* /dev/hdc*
62 DEV /dev/sd*
63 DEVICE /dev/disk/by-path/pci*
64 DEVICE partitions
65 ARRAY The ARRAY lines identify actual arrays. The second word on the
68 line may be the name of the device where the array is normally
69 assembled, such as /dev/md1 or /dev/md/backup. If the name does
70 not start with a slash ('/'), it is treated as being in
71 /dev/md/. Alternately the word <ignore> (complete with angle
72 brackets) can be given in which case any array which matches the
73 rest of the line will never be automatically assembled. If no
74 device name is given, mdadm will use various heuristics to
75 determine an appropriate name.
76 Subsequent words identify the array, or identify the array as a
78 member of a group. If multiple identities are given, then a com‐
79 ponent device must match ALL identities to be considered a
80 match. Each identity word has a tag, and equals sign, and some
81 value. The tags are:
82 uuid= The value should be a 128 bit uuid in hexadecimal, with
84 punctuation interspersed if desired. This must match the
85 uuid stored in the superblock.
86 name= The value should be a simple textual name as was given to
88 mdadm when the array was created. This must match the name
89 stored in the superblock on a device for that device to be
90 included in the array. Not all superblock formats support
91 names.
92 super-minor=
94 The value is an integer which indicates the minor number
95 that was stored in the superblock when the array was cre‐
96 ated. When an array is created as /dev/mdX, then the minor
97 number X is stored.
98 devices=
100 The value is a comma separated list of device names or
101 device name patterns. Only devices with names which match
102 one entry in the list will be used to assemble the array.
103 Note that the devices listed there must also be listed on a
104 DEVICE line.
105 level= The value is a raid level. This is not normally used to
107 identify an array, but is supported so that the output of
108 mdadm --examine --scan
110 can be use directly in the configuration file.
112 num-devices=
114 The value is the number of devices in a complete active
115 array. As with level= this is mainly for compatibility with
116 the output of
117 mdadm --examine --scan.
119 spares=
122 The value is a number of spare devices to expect the array
123 to have. The sole use of this keyword and value is as fol‐
124 lows: mdadm --monitor will report an array if it is found to
125 have fewer than this number of spares when --monitor starts
126 or when --oneshot is used.
127 spare-group=
130 The value is a textual name for a group of arrays. All
131 arrays with the same spare-group name are considered to be
132 part of the same group. The significance of a group of
133 arrays is that mdadm will, when monitoring the arrays, move
134 a spare drive from one array in a group to another array in
135 that group if the first array had a failed or missing drive
136 but no spare.
137 auto= This option is rarely needed with mdadm-3.0, particularly if
140 use with the Linux kernel v2.6.28 or later. It tells mdadm
141 whether to use partitionable array or non-partitionable
142 arrays and, in the absence of udev, how many partition
143 devices to create. From 2.6.28 all md array devices are
144 partitionable, hence this option is not needed.
145 The value of this option can be "yes" or "md" to indicate
147 that a traditional, non-partitionable md array should be
148 created, or "mdp", "part" or "partition" to indicate that a
149 partitionable md array (only available in linux 2.6 and
150 later) should be used. This later set can also have a num‐
151 ber appended to indicate how many partitions to create
152 device files for, e.g. auto=mdp5. The default is 4.
153 bitmap=
156 The option specifies a file in which a write-intent bitmap
157 should be found. When assembling the array, mdadm will pro‐
158 vide this file to the md driver as the bitmap file. This
159 has the same function as the --bitmap-file option to
160 --assemble.
161 metadata=
164 Specify the metadata format that the array has. This is
165 mainly recognised for comparability with the output of mdadm
166 -Es.
167 container=
170 Specify that this array is a member array of some container.
171 The value given can be either a path name in /dev, or a UUID
172 of the container array.
173 member=
176 Specify that this array is a member array of some container.
177 Each type of container has some way to enumerate member
178 arrays, often a simple sequence number. The value identi‐
179 fies which member of a container the array is. It will usu‐
180 ally accompany a "container=" word.
181 MAILADDR
184 The mailaddr line gives an E-mail address that alerts should be
185 sent to when mdadm is running in --monitor mode (and was given
186 the --scan option). There should only be one MAILADDR line and
187 it should have only one address.
188 MAILFROM
192 The mailfrom line (which can only be abbreviated to at least 5
193 characters) gives an address to appear in the "From" address for
194 alert mails. This can be useful if you want to explicitly set a
195 domain, as the default from address is "root" with no domain.
196 All words on this line are catenated with spaces to form the
197 address.
198 Note that this value cannot be set via the mdadm commandline.
200 It is only settable via the config file.
201 PROGRAM
204 The program line gives the name of a program to be run when
205 mdadm --monitor detects potentially interesting events on any of
206 the arrays that it is monitoring. This program gets run with
207 two or three arguments, they being the Event, the md device, and
208 possibly the related component device.
209 There should only be one program line and it should be give only
211 one program.
212 CREATE The create line gives default values to be used when creating
216 arrays and device entries for arrays. These include:
217 owner=
220 group= These can give user/group ids or names to use instead of
222 system defaults (root/wheel or root/disk).
223 mode= An octal file mode such as 0660 can be given to override the
225 default of 0600.
226 auto= This corresponds to the --auto flag to mdadm. Give yes, md,
228 mdp, part — possibly followed by a number of partitions — to
229 indicate how missing device entries should be created.
230 metadata=
233 The name of the metadata format to use if none is explicitly
234 given. This can be useful to impose a system-wide default
235 of version-1 superblocks.
236 symlinks=no
239 Normally when creating devices in /dev/md/ mdadm will create
240 a matching symlink from /dev/ with a name starting md or
241 md_. Give symlinks=no to suppress this symlink creation.
242 HOMEHOST
245 The homehost line gives a default value for the --homehost=
246 option to mdadm. There should normally be only one other word
247 on the line. It should either be a host name, or one of the
248 special words <system> and <ignore>. If <system> is given, then
249 the gethostname(2) systemcall is used to get the host name.
250 If <ignore> is given, then a flag is set so that when arrays are
252 being auto-assembled the checking of the recorded homehost is
253 disabled. If <ignore> is given it is also possible to give an
254 explicit name which will be used when creating arrays. This is
255 the only case when there can be more that one other word on the
256 HOMEHOST line.
257 When arrays are created, this host name will be stored in the
259 metadata. When arrays are assembled using auto-assembly, arrays
260 which do not record the correct homehost name in their metadata
261 will be assembled using a "foreign" name. A "foreign" name
262 alway ends with a digit string preceded by an underscore to dif‐
263 ferentiate it from any possible local name. e.g. /dev/md/1_1 or
264 /dev/md/home_0.
265 AUTO A list of names of metadata format can be given, each preceded
267 by a plus or minus sign. Also the word homehost is allowed as
268 is all preceded by plus or minus sign. all is usually last.
269 When mdadm is auto-assembling an array, either via --assemble or
271 --incremental and it finds metadata of a given type, it checks
272 that metadata type against those listed in this line. The first
273 match wins, where all matches anything. If a match is found
274 that was preceded by a plus sign, the auto assembly is allowed.
275 If the match was preceded by a minus sign, the auto assembly is
276 disallowed. If no match is found, the auto assembly is allowed.
277 If the metadata indicates that the array was created for this
279 host, and the word homehost appears before any other match, then
280 the array is treated as a valid candidate for auto-assembly.
281 This can be used to disable all auto-assembly (so that only
283 arrays explicitly listed in mdadm.conf or on the command line
284 are assembled), or to disable assembly of certain metadata types
285 which might be handled by other software. It can also be used
286 to disable assembly of all foreign arrays - normally such arrays
287 are assembled but given a non-deterministic name in /dev/md/.
288 The known metadata types are 0.90, 1.x, ddf, imsm.
290
293 DEVICE /dev/sd[bcdjkl]1
294 DEVICE /dev/hda1 /dev/hdb1
295 # /dev/md0 is known by its UUID.
297 ARRAY /dev/md0 UUID=3aaa0122:29827cfa:5331ad66:ca767371
298 # /dev/md1 contains all devices with a minor number of
299 # 1 in the superblock.
300 ARRAY /dev/md1 superminor=1
301 # /dev/md2 is made from precisely these two devices
302 ARRAY /dev/md2 devices=/dev/hda1,/dev/hdb1
303 # /dev/md4 and /dev/md5 are a spare-group and spares
305 # can be moved between them
306 ARRAY /dev/md4 uuid=b23f3c6d:aec43a9f:fd65db85:369432df
307 spare-group=group1
308 ARRAY /dev/md5 uuid=19464854:03f71b1b:e0df2edd:246cc977
309 spare-group=group1
310 # /dev/md/home is created if need to be a partitionable md array
311 # any spare device number is allocated.
312 ARRAY /dev/md/home UUID=9187a482:5dde19d9:eea3cc4a:d646ab8b
313 auto=part
314 MAILADDR root@mydomain.tld
316 PROGRAM /usr/sbin/handle-mdadm-events
317 CREATE group=system mode=0640 auto=part-8
318 HOMEHOST <system>
319 AUTO +1.x homehost -all
320
323 mdadm(8), md(4).
324 MDADM.CONF(5)