1SG_WRITE_SAME(8) SG3_UTILS SG_WRITE_SAME(8)
2
6 sg_write_same - send the SCSI WRITE SAME command
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9 sg_write_same [--16] [--32] [--anchor] [--grpnum=GN] [--help] [--in=IF]
10 [--lba=LBA] [--lbdata] [--num=NUM] [--pbdata] [--timeout=TO] [--unmap]
11 [--verbose] [--version] [--wrprotect=WPR] [--xferlen=LEN] DEVICE
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14 Send the SCSI WRITE SAME (10, 16 or 32 byte) command to DEVICE. This
15 command writes the given block NUM times to consecutive blocks on the
16 DEVICE starting at logical block address LBA.
17 The length of the block to be written multiple times is obtained from
19 the LEN argument, the length of the given input file IF, or by calling
20 READ CAPACITY(16) on DEVICE. The contents of the block to be written
21 are obtained from the input file IF or zeroes are used. If READ CAPAC‐
22 ITY(16) is called (which implies IF was not given) and the PROT_EN bit
23 is set then the last 8 bytes are set to 0xff.
24 By default WRITE SAME(10) is sent unless LBA (plus NUM) exceeds 32
26 bits, NUM exceeds 65535 or the --unmap option is given. In these cases
27 WRITE SAME(16) is sent.
28 Take care: The WRITE SAME(10, 16 and 32) commands interpret a NUM of
30 zero as write to the end of DEVICE. This utility defaults NUM to 1 .
31 The WRITE SAME commands have no IMMED bit so if NUM is large (or zero)
32 then an invocation of this utility could take a long time, potentially
33 as long as a FORMAT UNIT command. In such situations the command time‐
34 out value TO may need to be increased from its default value of 60 sec‐
35 onds.
36 As a precaution against an accidental 'sg_write_same /dev/sda' (for
38 example) overwriting LBA 0 on /dev/sda with zeroes, at least one of the
39 --in=IF, --lba=LBA or --num=NUM options must be given. Obviously this
40 utility can destroy a lot of user data so check the options carefully.
41 This utility is based SBC-3 draft revision 19 found at
43 http://www.t10.org .
44
46 Arguments to long options are mandatory for short options as well.
47 -S, --16
49 send a SCSI WRITE SAME (16) command to DEVICE. The default
50 action (in the absence of this option and the --32 option) is to
51 send a SCSI WRITE SAME (10) command.
52 -T, --32
54 send a SCSI WRITE SAME (32) command to DEVICE. The default
55 action (in the absence of this option and the --16 option) is to
56 send a SCSI WRITE SAME (10) command.
57 -a, --anchor
59 sets the 'Anchor' bit in the cdb. Ignored by WRITE SAME(10).
60 Introduced in sbc3r22.
61 -g, --grpnum=GN
63 sets the 'Group number' field to GN. Defaults to a value of
64 zero. GN should be a value between 0 and 31.
65 -h, --help
67 output the usage message then exit.
68 -i, --in=IF
70 read data (binary) from file named IF and use it as the data out
71 buffer for the SCSI WRITE SAME command. The length of the data
72 out buffer is --xferlen=LEN or, if that is not given, the length
73 of the IF file. If IF is "-" then stdin is read. If this option
74 is not given then 0x00 bytes are used as fill with the length of
75 the data out buffer obtained from --xferlen=LEN or by calling
76 READ CAPACITY(16). If the response to READ CAPACITY(16) has the
77 PROT_EN bit set then data out buffer size is modified accord‐
78 ingly with the last 8 bytes set to 0xff.
79 -l, --lba=LBA
81 where LBA is the logical block address to start the WRITE SAME
82 command. Defaults to lba 0 which is a dangerous block to over‐
83 write on a disk that is in use. Assumed to be in decimal unless
84 prefixed with '0x' or has a trailing 'h'.
85 -L, --lbdata
87 sets the LBDATA bit in the WRITE SAME cdb.
88 -n, --num=NUM
90 where NUM is the number of blocks, starting at LBA, to write the
91 data out buffer to. The default value for NUM is 1. The value
92 corresponds to the 'Number of logical blocks' field in the WRITE
93 SAME cdb. Note that a value of 0 in NUM is interpreted as write
94 the data out buffer on every block starting at LBA to the end of
95 the DEVICE.
96 -P, --pbdata
98 sets the PBDATA bit in the WRITE SAME cdb.
99 -t, --timeout=TO
101 where TO is the command timeout value in seconds. The default
102 value is 60 seconds. If NUM is large (or zero) a WRITE SAME com‐
103 mand may require considerably more time than 60 seconds to com‐
104 plete.
105 -U, --unmap
107 sets the UNMAP bit in the WRITE SAME(16 and 32) cdb. When this
108 option is given the default command becomes WRITE SAME(16) since
109 the WRITE SAME(10) command does not offer this bit (in SBC-3
110 draft revision 19). See UNMAP section below.
111 -v, --verbose
113 increase the degree of verbosity (debug messages).
114 -V, --version
116 output version string then exit.
117 -w, --wrprotect=WPR
119 sets the "Write protect" field in the WRITE SAME cdb to WPR. The
120 default value is zero. WPR should be a value between 0 and 7.
121 -x, --xferlen=LEN
123 where LEN is the data out buffer length. Defaults to the length
124 of the IF file or, if that is not given, then the READ CAPAC‐
125 ITY(16) command is called on the DEVICE and the 'Logical block
126 length in bytes' and the PROT_EN bit in the response are used to
127 determine the data out buffer length. If both this option and
128 the IF option are given and LEN exceeds the length of the IF
129 file then LEN is the data out buffer length with zeroes used as
130 pad bytes.
131
133 Thin provisioning is the sophisticated term used in SBC-3 revision 19
134 for the ability to mark blocks as unused. It is closely related to the
135 ATA DATA SET MANAGEMENT command with the "Trim" bit set. For large
136 storage arrays, it is a way to provision less physical storage than the
137 READ CAPACITY command reports is available, potentially allocating more
138 physical storage when WRITE commands require it. For flash memory it is
139 a way of potentially saving power (and perhaps access time) when it is
140 known large sections (or almost all) of the flash memory is not in use.
141 Support for thin provisioning is indicated by the TPE bit being set in
143 the READ CAPACITY(16) command response. That implies at least one of
144 the UNMAP or WRITE SAME(16) commands is implemented. If the UNMAP com‐
145 mand is implemented then the "Maximum unmap LBA count" and "Maximum
146 unmap block descriptor count" fields in the Block Limits VPD page
147 should both be greater than zero. The READ CAPACITY(16) command
148 response also contains a TPRZ bit which if set means that if unmapped
149 blocks are read then zeroes will be returned for the data (and if pro‐
150 tection information is active, 0xff bytes are returned for that).
151 In the cases of WRITE SAME(16) and WRITE SAME(32) when the Unmap bit is
153 set in the cdb then the data out buffer is also sent. Additionally the
154 data section of that data out buffer should be full of 0x0 bytes while
155 the data protection block, 8 bytes at the end if present, should be set
156 to 0xff bytes. If these conditions are not met and the TPRZ bit is set
157 then the Unmap bit is ignored and the data out buffer is written to the
158 DEVICE as if the Unmap bit was zero. In the absence of the --in=IF
159 option, this utility will attempt build a data out buffer that meets
160 the requirements for the Unmap bit in the cdb to be acted on by the
161 DEVICE.
162 Logical blocks may also be unmapped by the SCSI UNMAP and FORMAT UNIT
164 commands (see the sg_unmap and sg_format utilities). Support for thin
165 provisioning is indicated by the TPE bit in the response to the SCSI
166 READ CAPACITY (16) command (see the sg_readcap utility).
167
169 Various numeric arguments (e.g. LBA) may include multiplicative suf‐
170 fixes or be given in hexadecimal. See the "NUMERIC ARGUMENTS" section
171 in the sg3_utils(8) man page.
172
174 The exit status of sg_write_same is 0 when it is successful. Otherwise
175 see the sg3_utils(8) man page.
176
178 Written by Douglas Gilbert.
179
181 Report bugs to <dgilbert at interlog dot com>.
182
184 Copyright © 2009-2010 Douglas Gilbert
185 This software is distributed under a FreeBSD license. There is NO war‐
186 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
187 POSE.
188
190 sg_format,sg_get_lba_status,sg_readcap,sg_unmap(sg3_utils)
191sg3_utils-1.29 March 2010 SG_WRITE_SAME(8)