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] [--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 .
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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 -g, --grpnum=GN
59 sets the 'Group number' field to GN. Defaults to a value of
60 zero. GN should be a value between 0 and 31.
61 -h, --help
63 output the usage message then exit.
64 -i, --in=IF
66 read data (binary) from file named IF and use it as the data out
67 buffer for the SCSI WRITE SAME command. The length of the data
68 out buffer is --xferlen=LEN or, if that is not given, the length
69 of the IF file. If IF is "-" then stdin is read. If this option
70 is not given then 0x00 bytes are used as fill with the length of
71 the data out buffer obtained from --xferlen=LEN or by calling
72 READ CAPACITY(16). If the response to READ CAPACITY(16) has the
73 PROT_EN bit set then data out buffer size is modified accord‐
74 ingly with the last 8 bytes set to 0xff.
75 -l, --lba=LBA
77 where LBA is the logical block address to start the WRITE SAME
78 command. Defaults to lba 0 which is a dangerous block to over‐
79 write on a disk that is in use. Assumed to be in decimal unless
80 prefixed with '0x' or has a trailing 'h'.
81 -L, --lbdata
83 sets the LBDATA bit in the WRITE SAME cdb.
84 -n, --num=NUM
86 where NUM is the number of blocks, starting at LBA, to write the
87 data out buffer to. The default value for NUM is 1. The value
88 corresponds to the 'Number of logical blocks' field in the WRITE
89 SAME cdb. Note that a value of 0 in NUM is interpreted as write
90 the data out buffer on every block starting at LBA to the end of
91 the DEVICE.
92 -P, --pbdata
94 sets the PBDATA bit in the WRITE SAME cdb.
95 -t, --timeout=TO
97 where TO is the command timeout value in seconds. The default
98 value is 60 seconds. If NUM is large (or zero) a WRITE SAME com‐
99 mand may require considerably more time than 60 seconds to com‐
100 plete.
101 -U, --unmap
103 sets the UNMAP bit in the WRITE SAME(16 and 32) cdb. When this
104 option is given the default command becomes WRITE SAME(16) since
105 the WRITE SAME(10) command does not offer this bit (in SBC-3
106 draft revision 19). See UNMAP section below.
107 -v, --verbose
109 increase the degree of verbosity (debug messages).
110 -V, --version
112 output version string then exit.
113 -w, --wrprotect=WPR
115 sets the "Write protect" field in the WRITE SAME cdb to WPR. The
116 default value is zero. WPR should be a value between 0 and 7.
117 -x, --xferlen=LEN
119 where LEN is the data out buffer length. Defaults to the length
120 of the IF file or, if that is not given, then the READ CAPAC‐
121 ITY(16) command is called on the DEVICE and the 'Logical block
122 length in bytes' and the PROT_EN bit in the response are used to
123 determine the data out buffer length. If both this option and
124 the IF option are given and LEN exceeds the length of the IF
125 file then LEN is the data out buffer length with zeroes used as
126 pad bytes.
127
129 Thin provisioning is the sophisticated term used in SBC-3 revision 19
130 for the ability to mark blocks as unused. It is closely related to the
131 ATA DATA SET MANAGEMENT command with the "Trim" bit set. For large
132 storage arrays, it is a way to provision less physical storage than the
133 READ CAPACITY command reports is available, potentially allocating more
134 physical storage when WRITE commands require it. For flash memory it is
135 a way of potentially saving power (and perhaps access time) when it is
136 known large sections (or almost all) of the flash memory is not in use.
137 Support for thin provisioning is indicated by the TPE bit being set in
139 the READ CAPACITY(16) command response. That implies at least one of
140 the UNMAP or WRITE SAME(16) commands is implemented. If the UNMAP com‐
141 mand is implemented then the "Maximum unmap LBA count" and "Maximum
142 unmap block descriptor count" fields in the Block Limits VPD page
143 should both be greater than zero. The READ CAPACITY(16) command
144 response also contains a TPRZ bit which if set means that if unmapped
145 blocks are read then zeroes will be returned for the data (and if pro‐
146 tection information is active, 0xff bytes are returned for that).
147 In the cases of WRITE SAME(16) and WRITE SAME(32) when the Unmap bit is
149 set in the cdb then the data out buffer is also sent. Additionally the
150 data section of that data out buffer should be full of 0x0 bytes while
151 the data protection block, 8 bytes at the end if present, should be set
152 to 0xff bytes. If these conditions are not met and the TPRZ bit is set
153 then the Unmap bit is ignored and the data out buffer is written to the
154 DEVICE as if the Unmap bit was zero. In the absence of the --in=IF
155 option, this utility will attempt build a data out buffer that meets
156 the requirements for the Unmap bit in the cdb to be acted on by the
157 DEVICE.
158 Logical blocks may also be unmapped by the SCSI UNMAP and FORMAT UNIT
160 commands (see the sg_unmap and sg_format utilities). Support for thin
161 provisioning is indicated by the TPE bit in the response to the SCSI
162 READ CAPACITY (16) command (see the sg_readcap utility).
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165 Various numeric arguments (e.g. LBA) may include multiplicative suf‐
166 fixes or be given in hexadecimal. See the "NUMERIC ARGUMENTS" section
167 in the sg3_utils(8) man page.
168
170 The exit status of sg_write_same is 0 when it is successful. Otherwise
171 see the sg3_utils(8) man page.
172
174 Written by Douglas Gilbert.
175
177 Report bugs to <dgilbert at interlog dot com>.
178
180 Copyright © 2009 Douglas Gilbert
181 This software is distributed under a FreeBSD license. There is NO war‐
182 ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
183 POSE.
184
186 sg_format,sg_readcap,sg_unmap(sg3_utils)
187sg3_utils-1.28 June 2009 SG_WRITE_SAME(8)