1SG_DD(8) SG3_UTILS SG_DD(8)
2
6 sg_dd - copies data to and from files and devices. Specialised for
7 devices that understand the SCSI command set.
8
10 sg_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 [blk_sgio=0|1] [bpt=BPT] [cdbsz=6|10|12|16] [coe=0|1|2|3]
14 [coe_limit=CL] [dio=0|1] [odir=0|1] [retries=RETR] [sync=0|1]
15 [time=0|1] [verbose=VERB]
16
18 Copy data to and from any files. Specialized for "files" that are Linux
19 SCSI generic (sg) devices, raw devices or other devices that support
20 the SG_IO ioctl (which are only found in the lk 2.6 series). Similar
21 syntax and semantics to dd(1) but does not perform any conversions.
22 The first group in the synopsis above are "standard" Unix dd(1) oper‐
24 ands. The second group are extra options added by this utility. Both
25 groups are defined below.
26
28 blk_sgio=0 | 1
29 when set to 0, block devices (e.g. /dev/sda) are treated like
30 normal files (i.e. read(2) and write(2) are used for IO). When
31 set to 1, block devices are assumed to accept the SG_IO ioctl
32 and SCSI commands are issued for IO. This is only supported for
33 2.6 series kernels. Note that ATAPI devices (e.g. cd/dvd play‐
34 ers) use the SCSI command set but ATA disks do not (unless there
35 is a protocol conversion as often occurs in the USB mass storage
36 class). If the input or output device is a block device parti‐
37 tion (e.g. /dev/sda3) then setting this option causes the parti‐
38 tion information to be ignored (since access is directly to the
39 underlying device). Default is 0. See the 'sgio' flag.
40 bpt=BPT
42 each IO transaction will be made using BPT blocks (or less if
43 near the end of the copy). Default is 128 for block sizes less
44 that 2048 bytes, otherwise the default is 32. So for bs=512 the
45 reads and writes will each convey 64 KiB of data by default
46 (less if near the end of the transfer or memory restrictions).
47 When cd/dvd drives are accessed, the block size is typically
48 2048 bytes and bpt defaults to 32 which again implies 64 KiB
49 transfers. The block layer when the blk_sgio=1 option is used
50 has relatively low upper limits for transfer sizes (compared to
51 sg device nodes, see /sys/block/<dev_name>/queue/max_sectors_kb
52 ).
53 bs=BS where BS must be the block size of the physical device (if
55 either the input or output files are accessed via SCSI com‐
56 mands). Note that this differs from dd(1) which permits BS to be
57 an integral multiple. Default is 512 which is usually correct
58 for disks but incorrect for cdroms (which normally have 2048
59 byte blocks). For this utility the maximum size of each individ‐
60 ual IO operation is BS * BPT bytes.
61 cdbsz=6 | 10 | 12 | 16
63 size of SCSI READ and/or WRITE commands issued on sg device
64 names (or block devices when 'iflag=sgio' and/or 'oflag=sgio' is
65 given). Default is 10 byte SCSI command blocks (unless calcula‐
66 tions indicate that a 4 byte block number may be exceeded or BPT
67 is greater than 16 bits (65535), in which case it defaults to 16
68 byte SCSI commands).
69 coe=0 | 1 | 2 | 3
71 set to 1 or more for continue on error. Only applies to errors
72 on sg devices or block devices with the 'sgio' flag set. Thus
73 errors on other files will stop sg_dd. Default is 0 which
74 implies stop on any error. See the 'coe' flag for more informa‐
75 tion.
76 coe_limit=CL
78 where CL is the maximum number of consecutive bad blocks stepped
79 over (due to "coe>0") on reads before the copy terminates. This
80 only applies when IFILE is accessed via the SG_IO ioctl. The
81 default is 0 which is interpreted as no limit. This option is
82 meant to stop the copy soon after unrecorded media is detected
83 while still offering "continue on error" capability.
84 count=COUNT
86 copy COUNT blocks from IFILE to OFILE. Default is the minimum
87 (of IFILE and OFILE) number of blocks that sg devices report
88 from SCSI READ CAPACITY commands or that block devices (or their
89 partitions) report. Normal files are not probed for their size.
90 If skip=SKIP or skip=SEEK are given and the count is derived
91 (i.e. not explicitly given) then the derived count is scaled
92 back so that the copy will not overrun the device. If the file
93 name is a block device partition and COUNT is not given then the
94 size of the partition rather than the size of the whole device
95 is used. If COUNT is not given and cannot be derived then an
96 error message is issued and no copy takes place.
97 dio=0 | 1
99 default is 0 which selects indirect (buffered) IO on sg devices.
100 Value of 1 attempts direct IO which, if not available, falls
101 back to indirect IO and notes this at completion. If direct IO
102 is selected and /proc/scsi/sg/allow_dio has the value of 0 then
103 a warning is issued (and indirect IO is performed).
104 ibs=BS if given must be the same as BS given to 'bs=' option.
106 if=IFILE
108 read from IFILE instead of stdin. If IFILE is '-' then stdin is
109 read. Starts reading at the beginning of IFILE unless SKIP is
110 given.
111 iflag=FLAGS
113 where FLAGS is a comma separated list of one or more flags out‐
114 lined below. These flags are associated with IFILE and are
115 ignored when IFILE is stdin.
116 obs=BS if given must be the same as BS given to 'bs=' option.
118 odir=0 | 1
120 when set to one opens block devices (e.g. /dev/sda) with the
121 O_DIRECT flag. User memory buffers are aligned to the page size
122 when set. The default is 0 (i.e. the O_DIRECT flag is not used).
123 Has no effect on sg, normal or raw files. If blk_sgio is also
124 set then both are honoured: block devices are opened with the
125 O_DIRECT flag and SCSI commands are issued via the SG_IO ioctl.
126 of=OFILE
128 write to OFILE instead of stdout. If OFILE is '-' then writes to
129 stdout. If OFILE is /dev/null then no actual writes are per‐
130 formed. If OFILE is '.' (period) then it is treated the same
131 way as /dev/null (this is a shorthand notation). If OFILE exists
132 then it is _not_ truncated; it is overwritten from the start of
133 OFILE unless 'oflag=append' or SEEK is given.
134 oflag=FLAGS
136 where FLAGS is a comma separated list of one or more flags out‐
137 lined below. These flags are associated with OFILE and are
138 ignored when OFILE is /dev/null, '.' (period), or stdout.
139 retries=RETR
141 sometimes retries at the host are useful, for example when there
142 is a transport error. When RETR is greater than zero then SCSI
143 READs and WRITEs are retried on error, RETR times. Default value
144 is zero.
145 seek=SEEK
147 start writing SEEK bs-sized blocks from the start of OFILE.
148 Default is block 0 (i.e. start of file).
149 skip=SKIP
151 start reading SKIP bs-sized blocks from the start of IFILE.
152 Default is block 0 (i.e. start of file).
153 sync=0 | 1
155 when 1, does SYNCHRONIZE CACHE command on OFILE at the end of
156 the transfer. Only active when OFILE is a sg device file name or
157 a block device and 'blk_sgio=1' is given.
158 time=0 | 1
160 when 1, times transfer and does throughput calculation, out‐
161 putting the results (to stderr) at completion. When 0 (default)
162 doesn't perform timing.
163 verbose=VERB
165 as VERB increases so does the amount of debug output sent to
166 stderr. Default value is zero which yields the minimum amount
167 of debug output. A value of 1 reports extra information that is
168 not repetitive. A value 2 reports cdbs and responses for SCSI
169 commands that are not repetitive (i.e. other that READ and
170 WRITE). Error processing is not considered repetitive. Values of
171 3 and 4 yield output for all SCSI commands (and Unix read() and
172 write() calls) so there can be a lot of output. This only
173 occurs for scsi generic (sg) devices and block devices when the
174 'blk_sgio=1' option is set.
175 --help outputs usage message and exits.
177 --version
179 outputs version number information and exits.
180
182 Here is a list of flags and their meanings:
183 append causes the O_APPEND flag to be added to the open of OFILE. For
185 regular files this will lead to data appended to the end of any
186 existing data. Cannot be used together with the seek=SEEK
187 option as they conflict. The default action of this utility is
188 to overwrite any existing data from the beginning of the file
189 or, if SEEK is given, starting at block SEEK. Note that attempt‐
190 ing to 'append' to a device file (e.g. a disk) will usually be
191 ignored or may cause an error to be reported.
192 coe continue on error. Only active for sg devices and block devices
194 that have the 'sgio' flag set. 'iflag=coe oflag=coe' and 'coe=1'
195 are equivalent. Use this flag twice (e.g. 'iflag=coe,coe') to
196 have the same action as the 'coe=2'. A medium, hardware or blank
197 check error while reading will re-read blocks prior to the bad
198 block, then try to recover the bad block, supplying zeros if
199 that fails, and finally reread the blocks after the bad block. A
200 medium, hardware or blank check error while writing is noted and
201 ignored. The recovery of the bad block when reading uses the
202 SCSI READ LONG command if 'coe' given twice or more (also with
203 the command line option 'coe=2'). Further, the READ LONG will
204 set its CORRCT bit if 'coe' given thrice. SCSI disks may auto‐
205 matically try and remap faulty sectors (see the AWRE and ARRE in
206 the read write error recovery mode page (the sdparm utility to
207 access and possibly change these attributes)). Errors occurring
208 on other files types will stop sg_dd. Error messages are sent
209 to stderr. This flag is similar to 'conv=noerror' in the dd(1)
210 utility. See note about READ LONG below.
211 direct causes the O_DIRECT flag to be added to the open of IFILE and/or
213 OFILE. This flag requires some memory alignment on IO. Hence
214 user memory buffers are aligned to the page size. Has no effect
215 on sg, normal or raw files. If 'iflag=sgio' and/or 'oflag=sgio'
216 is also set then both are honoured: block devices are opened
217 with the O_DIRECT flag and SCSI commands are issued via the
218 SG_IO ioctl.
219 dpo set the DPO bit (disable page out) in SCSI READ and WRITE com‐
221 mands. Not supported for 6 byte cdb variants of READ and WRITE.
222 Indicates that data is unlikely to be required to stay in device
223 (e.g. disk) cache. May speed media copy and/or cause a media
224 copy to have less impact on other device users.
225 dsync causes the O_SYNC flag to be added to the open of IFILE and/or
227 OFILE. The 'd' is prepended to lower confusion with the
228 'sync=0|1' option which has another action (i.e. a synchronisa‐
229 tion to media at the end of the transfer).
230 excl causes the O_EXCL flag to be added to the open of IFILE and/or
232 OFILE.
233 fua causes the FUA (force unit access) bit to be set in SCSI READ
235 and/or WRITE commands. This only has an effect with sg devices
236 or block devices that have the 'sgio' flag set. The 6 byte vari‐
237 ants of the SCSI READ and WRITE commands do not support the FUA
238 bit.
239 sgio causes block devices to be accessed via the SG_IO ioctl rather
241 than standard UNIX read() and write() commands. When the SG_IO
242 ioctl is used the SCSI READ and WRITE commands are used directly
243 to move data. sg devices always use the SG_IO ioctl. This flag
244 offers finer grain control compared to the otherwise identical
245 'blk_sgio=1' option.
246
248 Here are some retired options that are still present:
249 append=0 | 1
251 when set, equivalent to 'oflag=append'. When clear the action is
252 to overwrite the existing file (if it exists); this is the
253 default. See the 'append' flag.
254 fua=0 | 1 | 2 | 3
256 force unit access bit. When 3, fua is set on both IFILE and
257 OFILE; when 2, fua is set on IFILE;, when 1, fua is set on
258 OFILE; when 0 (default), fua is cleared on both. See the 'fua'
259 flag.
260
262 Block devices (e.g. /dev/sda and /dev/hda) can be given for IFILE. If
263 neither '-iflag=direct', 'iflag=sgio' nor 'blk_sgio=1' is given then
264 normal block IO involving buffering and caching is performed. If only
265 '-iflag=direct' is given then the buffering and caching is bypassed
266 (this is applicable to both SCSI devices and ATA disks). If
267 'iflag=sgio' or 'blk_sgio=1' is given then the SG_IO ioctl is used on
268 the given file causing SCSI commands to be sent to the device and that
269 also bypasses most of the actions performed by the block layer (this is
270 only applicable to SCSI devices, not ATA disks). The same applies for
271 block devices given for OFILE.
272 COUNT, SKIP, SEEK, BPT and BS may include one of these multiplicative
274 suffixes: c C *1; w W *2; b B *512; k K KiB *1,024; KB *1,000; m M MiB
275 *1,048,576; MB *1,000,000 . This pattern continues for "G", "T" and
276 "P". The latter two suffixes can only be used for COUNT, SKIP and SEEK.
277 Also a suffix of the form "x<n>" multiplies the leading number by <n>.
278 These multiplicative suffixes are compatible with GNU's dd command
279 (since 2002) which claims compliance with SI and with IEC 60027-2.
280 Alternatively numerical values can be given in hexadecimal preceded by
282 either "0x" or "0X" (or with a trailing "h" or "H"). When hex numbers
283 are given, multipliers cannot be used.
284 The COUNT, SKIP and SEEK arguments can take 64 bit values (i.e. very
286 big numbers). Other values are limited to what can fit in a signed 32
287 bit number.
288 Data usually gets to the user space in a 2 stage process: first the
290 SCSI adapter DMAs into kernel buffers and then the sg driver copies
291 this data into user memory (write operations reverse this sequence).
292 This is called "indirect IO" and there is a 'dio' option to select
293 "direct IO" which will DMA directly into user memory. Due to some
294 issues "direct IO" is disabled in the sg driver and needs a configura‐
295 tion change to activate it. This is typically done with 'echo 1 >
296 /proc/scsi/sg/allow_dio'.
297 All informative, warning and error output is sent to stderr so that
299 dd's output file can be stdout and remain unpolluted. If no options are
300 given, then the usage message is output and nothing else happens.
301 Even if READ LONG succeeds on a "bad" block when 'coe=2' (or 'coe=3')
303 is given, the recovered data may not be useful. There are no guarantees
304 that the user data will appear "as is" in the first 512 bytes.
305 A raw device must be bound to a block device prior to using sg_dd. See
307 raw(8) for more information about binding raw devices. To be safe, the
308 sg device mapping to SCSI block devices should be checked with 'cat
309 /proc/scsi/scsi', or sg_map before use.
310 Disk partition information can often be found with fdisk(8) [the "-ul"
312 argument is useful in this respect].
313 For sg devices (and block devices when blk_sgio=1 is given) this util‐
315 ity issues SCSI READ and WRITE (SBC) commands which are appropriate for
316 disks and reading from CD/DVD drives. Those commands are not formatted
317 correctly for tape devices so sg_dd should not be used on tape devices.
318 If the largest block address of the requested transfer exceeds a 32 bit
319 block number (i.e 0xffff) then a warning is issued and the sg device is
320 accessed via SCSI READ(16) and WRITE(16) commands.
321 The attributes of a block device (partition) are ignored when
323 'blk_sgio=1' is used. Hence the whole device is read (rather than just
324 the second partition) by this invocation:
325 sg_dd if=/dev/sdb2 blk_sgio=1 of=t bs=512
327
329 Looks quite similar in usage to dd:
330 sg_dd if=/dev/sg0 of=t bs=512 count=1MB
332 This will copy 1 million 512 byte blocks from the device associated
334 with /dev/sg0 (which should have 512 byte blocks) to a file called t.
335 Assuming /dev/sda and /dev/sg0 are the same device then the above is
336 equivalent to:
337 dd if=/dev/sda iflag=direct of=t bs=512 count=1000000
339 although dd's speed may improve if bs was larger and count was suitably
341 reduced. The use of the 'iflag=direct' option bypasses the buffering
342 and caching that is usually done on a block device.
343 Using a raw device to do something similar on a ATA disk:
345 raw /dev/raw/raw1 /dev/hda
347 sg_dd if=/dev/raw/raw1 of=t bs=512 count=1MB
348 To copy a SCSI disk partition to an ATA disk partition:
350 raw /dev/raw/raw2 /dev/hda3
352 sg_dd if=/dev/sg0 skip=10123456 of=/dev/raw/raw2 bs=512
353 This assumes a valid partition is found on the SCSI disk at the given
355 skip block address (past the 5 GB point of that disk) and that the par‐
356 tition goes to the end of the SCSI disk. An explicit count is probably
357 a safer option. The partition is copied to /dev/hda3 which is an offset
358 into the ATA disk /dev/hda . The exact number of blocks read from
359 /dev/sg0 are written to /dev/hda (i.e. no padding).
360 To time a streaming read of the first 1 GB (2 ** 30 bytes) on a disk
362 this utility could be used:
363 sg_dd if=/dev/sg0 of=/dev/null bs=512 count=2m time=1
365 On completion this will output a line like: "time to transfer data was
367 18.779506 secs, 57.18 MB/sec". The "MB/sec" in this case is 1,000,000
368 bytes per second.
369
371 The signal handling has been borrowed from dd: SIGINT, SIGQUIT and SIG‐
372 PIPE output the number of remaining blocks to be transferred and the
373 records in + out counts; then they have their default action. SIGUSR1
374 causes the same information to be output yet the copy continues. All
375 output caused by signals is sent to stderr.
376
378 The exit status of sg_dd is 0 when it is successful. Otherwise see the
379 sg3_utils(8) man page. Since this utility works at a higher level than
380 individual commands, and there are 'coe' and 'retries' flags, individ‐
381 ual SCSI command failures do not necessary cause the process to exit.
382
384 Written by Doug Gilbert and Peter Allworth.
385
387 Report bugs to <dgilbert at interlog dot com>.
388
390 Copyright © 2000-2007 Douglas Gilbert
391 This software is distributed under the GPL version 2. There is NO war‐
392 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
393 POSE.
394
396 There is a web page discussing sg_dd at
397 http://www.torque.net/sg/sg_dd.html
398 A POSIX threads version of this utility called sgp_dd is in the
400 sg3_utils package. Another version from that package is called sgm_dd
401 and it uses memory mapped IO to speed transfers from sg devices.
402 The lmbench package contains lmdd which is also interesting. For moving
404 data to and from tapes see dt which is found at http://www.scsi‐
405 faq.org/RMiller_Tools/index.html
406 To change mode parameters that effect a SCSI device's caching and error
408 recovery see sdparm(sdparm)
409 See also raw(8), dd(1), ddrescue(GNU)
411sg3_utils-1.23 January 2007 SG_DD(8)