1SGP_DD(8) SG3_UTILS SGP_DD(8)
2
6 sgp_dd - copies data to and from files and devices. Specialized for
7 devices that understand the SCSI command set.
8
10 sgp_dd [bs=BS] [count=COUNT] [ibs=BS] [if=IFILE] [iflag=FLAGS] [obs=BS]
11 [of=OFILE] [oflag=FLAGS] [seek=SEEK] [skip=SKIP] [--help] [--version]
12 [bpt=BPT] [coe=0|1] [cdbsz=6|10|12|16] [deb=VERB] [dio=0|1] [sync=0|1]
14 [thr=THR] [time=0|1] [verbose=VERB]
15
17 Copy data to and from any files. Specialised for "files" that are Linux
18 SCSI generic (sg) and raw devices. Similar syntax and semantics to
19 dd(1) but does not perform any conversions. Uses POSIX threads to
20 increase the amount of parallelism. This improves speed in some cases.
21 The first group in the synopsis above are "standard" Unix dd(1) oper‐
23 ands. The second group are extra options added by this utility. Both
24 groups are defined below.
25
27 bpt=BPT
28 each IO transaction will be made using BPT blocks (or less if
29 near the end of the copy). Default is 128 for block sizes less
30 that 2048 bytes, otherwise the default is 32. So for bs=512 the
31 reads and writes will each convey 64 KiB of data by default
32 (less if near the end of the transfer or memory restrictions).
33 When cd/dvd drives are accessed, the block size is typically
34 2048 bytes and bpt defaults to 32 which again implies 64 KiB
35 transfers.
36 bs=BS where BS must be the block size of the physical device. Note
38 that this differs from dd(1) which permits 'bs' to be an inte‐
39 gral multiple of the actual device block size. Default is 512
40 which is usually correct for disks but incorrect for cdroms
41 (which normally have 2048 byte blocks).
42 cdbsz=6 | 10 | 12 | 16
44 size of SCSI READ and/or WRITE commands issued on sg device
45 names. Default is 10 byte SCSI command blocks (unless calcula‐
46 tions indicate that a 4 byte block number may be exceeded, in
47 which case it defaults to 16 byte SCSI commands).
48 coe=0 | 1
50 set to 1 for continue on error. Only applies to errors on sg
51 devices. Thus errors on other files will stop sgp_dd. Default
52 is 0 which implies stop on any error. See the 'coe' flag for
53 more information.
54 count=COUNT
56 copy COUNT blocks from IFILE to OFILE. Default is the minimum
57 (of IFILE and OFILE) number of blocks that sg devices report
58 from SCSI READ CAPACITY commands or that block devices (or their
59 partitions) report. Normal files are not probed for their size.
60 If skip=SKIP or skip=SEEK are given and the count is deduced
61 (i.e. not explicitly given) then that count is scaled back so
62 that the copy will not overrun the device. If the file name is a
63 block device partition and COUNT is not given then the size of
64 the partition rather than the size of the whole device is used.
65 If COUNT is not given and cannot be deduced then an error mes‐
66 sage is issued and no copy takes place.
67 deb=VERB
69 outputs debug information. If VERB is 0 (default) then there is
70 minimal debug information and as VERB increases so does the
71 amount of debug (max debug output when VERB is 9).
72 dio=0 | 1
74 default is 0 which selects indirect IO. Value of 1 attempts
75 direct IO which, if not available, falls back to indirect IO and
76 notes this at completion. If direct IO is selected and
77 /proc/scsi/sg/allow_dio has the value of 0 then a warning is
78 issued (and indirect IO is performed)
79 ibs=BS if given must be the same as BS given to 'bs=' option.
81 if=IFILE
83 read from IFILE instead of stdin. If IFILE is '-' then stdin is
84 read. Starts reading at the beginning of IFILE unless SKIP is
85 given.
86 iflag=FLAGS
88 where FLAGS is a comma separated list of one or more flags out‐
89 lined below. These flags are associated with IFILE and are
90 ignored when IFILE is stdin.
91 obs=BS if given must be the same as BS given to 'bs=' option.
93 of=OFILE
95 write to OFILE instead of stdout. If OFILE is '-' then writes to
96 stdout. If OFILE is /dev/null then no actual writes are per‐
97 formed. If OFILE is '.' (period) then it is treated the same
98 way as /dev/null (this is a shorthand notation). If OFILE exists
99 then it is _not_ truncated; it is overwritten from the start of
100 OFILE unless 'oflag=append' or SEEK is given.
101 oflag=FLAGS
103 where FLAGS is a comma separated list of one or more flags out‐
104 lined below. These flags are associated with OFILE and are
105 ignored when OFILE is /dev/null, '.' (period), or stdout.
106 seek=SEEK
108 start writing SEEK bs-sized blocks from the start of OFILE.
109 Default is block 0 (i.e. start of file).
110 skip=SKIP
112 start reading SKIP bs-sized blocks from the start of IFILE.
113 Default is block 0 (i.e. start of file).
114 sync=0 | 1
116 when 1, does SYNCHRONIZE CACHE command on OFILE at the end of
117 the transfer. Only active when OFILE is a sg device file name.
118 thr=THR
120 where THR is the number or worker threads (default 4) that
121 attempt to copy in parallel. Minimum is 1 and maximum is 16.
122 time=0 | 1
124 when 1, the transfer is timed and throughput calculation is per‐
125 formed, outputting the results (to stderr) at completion. When 0
126 (default) no timing is performed.
127 verbose=VERB
129 increase verbosity. Same as deb=VERB. Added for compatibility
130 with sg_dd and sgm_dd.
131 --help outputs usage message and exits.
133 --version
135 outputs version number information and exits.
136
138 Here is a list of flags and their meanings:
139 append causes the O_APPEND flag to be added to the open of OFILE. For
141 normal files this will lead to data appended to the end of any
142 existing data. Cannot be used together with the seek=SEEK
143 option as they conflict. The default action of this utility is
144 to overwrite any existing data from the beginning of the file
145 or, if SEEK is given, starting at block SEEK. Note that attempt‐
146 ing to 'append' to a device file (e.g. a disk) will usually be
147 ignored or may cause an error to be reported.
148 coe continue on error. When given with 'iflag=', an error that is
150 detected in a single SCSI command (typically 'bpt' blocks) is
151 noted (by an error message sent to stderr), then zeros are sub‐
152 stituted into the buffer for the corresponding write operation
153 and the copy continues. Note that the sg_dd utility is more
154 sophisticated in such error situations when 'iflag=coe'. When
155 given with 'oflag=', any error reported by a SCSI WRITE command
156 is reported to stderr and the copy continues (as if nothing went
157 wrong).
158 direct causes the O_DIRECT flag to be added to the open of IFILE and/or
160 OFILE. This flag requires some memory alignment on IO. Hence
161 user memory buffers are aligned to the page size. Has no effect
162 on sg, normal or raw files.
163 dpo set the DPO bit (disable page out) in SCSI READ and WRITE com‐
165 mands. Not supported for 6 byte cdb variants of READ and WRITE.
166 Indicates that data is unlikely to be required to stay in device
167 (e.g. disk) cache. May speed media copy and/or cause a media
168 copy to have less impact on other device users.
169 dsync causes the O_SYNC flag to be added to the open of IFILE and/or
171 OFILE. The 'd' is prepended to lower confusion with the
172 'sync=0|1' option which has another action (i.e. a synchronisa‐
173 tion to media at the end of the transfer).
174 excl causes the O_EXCL flag to be added to the open of IFILE and/or
176 OFILE.
177 fua causes the FUA (force unit access) bit to be set in SCSI READ
179 and/or WRITE commands. This only has effect with sg devices. The
180 6 byte variants of the SCSI READ and WRITE commands do not sup‐
181 port the FUA bit. Only active for sg device file names.
182
184 Here are some retired options that are still present:
185 coe=0 | 1
187 continue on error is 0 (off) by default. When it is 1, it is
188 equivalent to 'iflag=coe oflag=coe' described in the FLAGS sec‐
189 tion above. Similar to 'conv=noerror' in dd(1) utility. Default
190 is 0 which implies stop on error. More advanced coe=1 processing
191 on reads is performed by the sg_dd utility.
192 fua=0 | 1 | 2 | 3
195 force unit access bit. When 3, fua is set on both IFILE
196 and OFILE; when 2, fua is set on IFILE;, when 1, fua is
197 set on OFILE; when 0 (default), fua is cleared on both.
198 See the 'fua' flag.
199
201 A raw device must be bound to a block device prior to using
202 sgp_dd. See raw(8) for more information about binding raw
203 devices. To be safe, the sg device mapping to SCSI block devices
204 should be checked with 'cat /proc/scsi/scsi' before use.
205 Raw device partition information can often be found with
207 fdisk(8) [the "-ul" argument is useful in this respect].
208 COUNT, SKIP, SEEK, BPT and BS may include one of these multi‐
210 plicative suffixes: c C *1; w W *2; b B *512; k K KiB *1,024; KB
211 *1,000; m M MiB *1,048,576; MB *1,000,000 . This pattern contin‐
212 ues for "G", "T" and "P". The latter two suffixes can only be
213 used for COUNT, SKIP and SEEK. Also a suffix of the form "x<n>"
214 multiplies the leading number by <n>. These multiplicative suf‐
215 fixes are compatible with GNU's dd command (since 2002) which
216 claims compliance with SI and with IEC 60027-2.
217 Alternatively numerical values can be given in hexadecimal pre‐
219 ceded by either "0x" or "0X". When hex numbers are given, multi‐
220 pliers cannot be used.
221 The COUNT, SKIP and SEEK arguments can take 64 bit values (i.e.
223 very big numbers). Other values are limited to what can fit in a
224 signed 32 bit number.
225 Data usually gets to the user space in a 2 stage process: first
227 the SCSI adapter DMAs into kernel buffers and then the sg driver
228 copies this data into user memory (write operations reverse this
229 sequence). This is called "indirect IO" and there is a 'dio'
230 option to select "direct IO" which will DMA directly into user
231 memory. Due to some issues "direct IO" is disabled in the sg
232 driver and needs a configuration change to activate it.
233 All informative, warning and error output is sent to stderr so
235 that dd's output file can be stdout and remain unpolluted. If no
236 options are given, then the usage message is output and nothing
237 else happens.
238 Why use sgp_dd? Because in some cases it is twice as fast as dd
240 (mainly with sg devices, raw devices give some improvement).
241 Another reason is that big copies fill the block device caches
242 which has a negative impact on other machine activity.
243
245 The signal handling has been borrowed from dd: SIGINT, SIGQUIT
246 and SIGPIPE output the number of remaining blocks to be trans‐
247 ferred and the records in + out counts; then they have their
248 default action. SIGUSR1 causes the same information to be out‐
249 put yet the copy continues. All output caused by signals is
250 sent to stderr.
251
253 Looks quite similar in usage to dd:
254 sgp_dd if=/dev/sg0 of=t bs=512 count=1MB
256 This will copy 1 million 512 byte blocks from the device associ‐
258 ated with /dev/sg0 (which should have 512 byte blocks) to a file
259 called t. Assuming /dev/sda and /dev/sg0 are the same device
260 then the above is equivalent to:
261 dd if=/dev/sda of=t bs=512 count=1000000
263 although dd's speed may improve if bs was larger and count was
265 correspondingly scaled. Using a raw device to do something simi‐
266 lar on a ATA disk:
267 raw /dev/raw/raw1 /dev/hda
269 sgp_dd if=/dev/raw/raw1 of=t bs=512 count=1MB
270 To copy a SCSI disk partition to an ATA disk partition:
272 raw /dev/raw/raw2 /dev/hda3
274 sgp_dd if=/dev/sg0 skip=10123456 of=/dev/raw/raw2 bs=512
275 This assumes a valid partition is found on the SCSI disk at the
277 given skip block address (past the 5 GB point of that disk) and
278 that the partition goes to the end of the SCSI disk. An explicit
279 count is probably a safer option.
280 To do a fast copy from one SCSI disk to another one with similar
282 geometry (stepping over errors on the source disk):
283 sgp_dd if=/dev/sg0 of=/dev/sg1 bs=512 coe=1
285
287 The exit status of sgp_dd is 0 when it is successful. Otherwise
288 see the sg3_utils(8) man page. Since this utility works at a
289 higher level than individual commands, and there are 'coe' and
290 'retries' flags, individual SCSI command failures do not neces‐
291 sary cause the process to exit.
292
294 Written by Doug Gilbert and Peter Allworth.
295
297 Report bugs to <dgilbert at interlog dot com>.
298
300 Copyright © 2000-2007 Douglas Gilbert
301 This software is distributed under the GPL version 2. There is
302 NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PAR‐
303 TICULAR PURPOSE.
304
306 A simpler, non-threaded version of this utility but with more
307 advanced "continue on error" logic is called sg_dd and is also
308 found in the sg3_utils package. The lmbench package contains
309 lmdd which is also interesting. raw(8), dd(1)
310sg3_utils-1.23 January 2007 SGP_DD(8)