sg_format man page on Alpinelinux
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SG_FORMAT(8) SG3_UTILS SG_FORMAT(8)
NAME
sg_format - format or resize a SCSI disk (perhaps change its block
size)
SYNOPSIS
sg_format [--cmplst={0|1}] [--count=COUNT] [--dcrt] [--early] [--fmt‐
pinfo=FPI] [--format] [--help] [--long] [--pfu=PFU] [--pie=PIE]
[--pinfo] [--poll=PT] [--resize] [--rto_req] [--security] [--six]
[--size=SIZE] [--verbose] [--version] [--wait] DEVICE
DESCRIPTION
Not all SCSI direct access devices need to be formatted and some have
vendor specific formatting procedures. SCSI disks with rotating media
are probably the largest group that do support a 'standard' format
operation. They are typically factory formatted to a block size of 512
bytes with the largest number of blocks that the manufacturer recom‐
mends. The manufacturer's recommendation typically leaves aside a cer‐
tain number of tracks, spread across the media, for reassignment of
blocks to logical block addresses during the life of the disk.
This utility can format modern SCSI disks and potentially change their
block size (if permitted) and the block count (i.e. number of accessi‐
ble blocks on the media also known as "resizing"). Resizing a disk to
less than the manufacturer's recommended block count is sometimes
called "short stroking" (see NOTES section). Resizing the block count
while not changing the block size may not require a format operation.
The SBC-2 standard (see www.t10.org) has obsoleted the "format device"
mode page. Many of the low level details found in that mode page are
now left up to the discretion of the manufacturer.
When this utility is used without options (i.e. it is only given a
DEVICE argument) it prints out the existing block size and block count
derived from two sources. These two sources are a block descriptor in
the response to a MODE SENSE command and the response to a READ CAPAC‐
ITY command. The reason for this double check is to detect a "format
corrupt" state (see NOTES section). This usage will not modify the
disk.
When this utility is used with the "--format" (or "-F") option it will
attempt to format the given DEVICE. There is a 10 second pause during
which time the user is invited twice (5 seconds apart) to abort sg_for‐
mat. This occurs just prior the SCSI FORMAT UNIT command being issued.
See the NOTES section for more information.
Protection information is optional and is made up of 8 additional bytes
associated with each logical block. Four protection types are defined
with protection type 0 being no additional protection bytes. See the
PROTECTION INFORMATION section below for more information.
OPTIONS
Arguments to long options are mandatory for short options as well. The
options are arranged in alphabetical order based on the long option
name.
-C, --cmplst={0|1}
sets the CMPLST ("complete list") bit in the FORMAT UNIT cdb to
0 or 1. The default is 1 in which case the existing GLIST
(grown list) is ignored. If the value is 0 then the existing
GLIST is taken into account. See the LISTS section below. In
most cases this bit should be left set; some MO disk drives need
this bit cleared.
-c, --count=COUNT
where COUNT is the number of blocks to be formatted or media to
be resized to. Can be used with either --format or --resize.
With --format this option need not be given in which case it is
assumed to be zero. With --format the interpretation of COUNT
is:
(COUNT > 0) : only format the first COUNT blocks and READ
CAPACITY will report COUNT blocks after format
(COUNT = 0) and block size unchanged : use existing block
count
(COUNT = 0) and block size changed : recommended maximum block
count for new block size
(COUNT = -1) : use recommended maximum block count
(COUNT < -1) : illegal
With --resize this option must be given and COUNT has this
interpretation:
(COUNT > 0) : after resize READ CAPACITY will report COUNT
blocks
(COUNT = 0) : after resize READ CAPACITY will report 0 blocks
(COUNT = -1) : after resize READ CAPACITY will report its
maximum number of blocks
(COUNT < -1) : illegal
In both cases if the given COUNT exceeds the maximum number of
blocks (for the block size) then the disk reports an error. See
NOTES section below.
-D, --dcrt
this option sets the DCRT bit in the FORMAT UNIT command's
parameter list header. It will "disable certification". Certifi‐
cation verifies that blocks are usable during the format
process. Using this option may speed the format. The default
action of this utility (i.e. when this option is not given) is
to clear the DCRT bit thereby requesting "media certification".
When the DCRT bit is set, the FOV bit must also be set hence
sg_format does that.
-e, --early
during a format operation, The default action of this utility is
to poll the disk every 60 seconds to determine the progress of
the format operation until it is finished. When this option is
given this utility will exit "early", that is as soon as the
format operation has commenced. Then the user can monitor the
progress of the ongoing format operation with other utilities
(e.g. sg_turs(8) or sg_requests(8)). This option and --wait are
mutually exclusive.
-f, --fmtpinfo=FPI
sets the FMTPINFO field in the FORMAT UNIT cdb to a value
between 0 and 3. The default value is 0. The FMTPINFO field
from SBC-3 revision 16 is a 2 bit field (bits 7 and 6 of byte 1
in the cdb). Prior to that it was a single bit field (bit 7 of
byte 1 in the cdb) and there was an accompanying bit called
RTO_REQ (bit 6 of byte 1 in the cdb). The deprecated options
"--pinfo" and "--rto-req" represent the older usage. This option
should be used in their place. See the PROTECTION INFORMATION
section below for more information.
-F, --format
issue a SCSI FORMAT UNIT command. This will destroy all the
data held on the media. This option is required to change the
block size of a disk. The user is given a 10 second count down
to ponder the wisdom of doing this, during which time control-C
(amongst other Unix commands) can be used to kill this process
before it does any damage. See NOTES section for implementation
details and EXAMPLES section for typical use.
-h, --help
print out the usage information then exit.
-l, --long
the default action of this utility is to assume 32 bit logical
block addresses. With 512 byte block size this permits more than
2 terabytes (almost 2 ** 41 bytes) on a single disk. This option
selects commands and parameters that allow for 64 bit logical
block addresses. Specifically this option sets the "longlba"
flag in the MODE SENSE (10) command and uses READ CAPACITY (16)
rather than READ CAPACITY (10). If this option is not given and
READ CAPACITY (10) or MODE SELECT detects a disk the needs more
than 32 bits to represent its logical blocks then it is set
internally. This option does not set the LONGLIST bit in the
FORMAT UNIT command. The LONGLIST bit is set as required depend‐
ing other parameters (e.g. when '--pie=PIE' is greater than
zero).
-P, --pfu=PFU
sets the "Protection Field Usage" field in the parameter block
associated with a FORMAT UNIT command to PFU. The default value
is 0, the only other defined value currently is 1. See the PRO‐
TECTION INFORMATION section below for more information.
-q, --pie=PIE
sets the "Protection Interval Exponent" field in the parameter
block associated with a FORMAT UNIT command to PIE. The default
value is 0. This field first appeared in SBC-3 revision 18.
-p, --pinfo
this option is deprecated, use the --fmtpinfo=FPI option
instead. If used, then it sets bit 7 of byte 1 in the FORMAT
UNIT cdb and that is equivalent to setting --fmtpinfo=2. [So if
--pinfo is used (plus --fmtpinfo=FPI and --pfu=PFU are not given
or their arguments are 0) then protection type 1 is selected.]
-x, --poll=PT
where PT is the type of poll used. If PT is 0 then a TEST UNIT
READY command is used, otherwise a REQUEST SENSE command is
used. The default is currently 0 but this will change to 1 in
the near future. See the NOTES sections below.
-r, --resize
rather than format the disk, it can be resized. This means
changing the number of blocks on the device reported by the READ
CAPACITY command. This option should be used with the
--count=COUNT option. The contents of all logical blocks on the
media remain unchanged when this option is used. This means that
any resize operation can be reversed. This option cannot be used
together with either --format or a --size=SIZE whose argument is
different to the existing block size.
-R, --rto_req
The option is deprecated, use the --fmtpinfo=FPI option instead.
If used, then it sets bit 6 of byte 1 in the FORMAT UNIT cdb.
-S, --security
sets the "Security Initialization" (SI) bit in the FORMAT UNIT
command's initialization pattern descriptor within the parameter
list. According to SBC-3 the default initialization pattern
"shall be written using a security erasure write technique". See
the NOTES section on the SCSI SANITIZE command.
-6, --six
Use 6 byte variants of MODE SENSE and MODE SELECT. The default
action is to use the 10 byte variants. Some MO drives need this
option set when doing a format.
-s, --size=SIZE
where SIZE is the block size (i.e. number of bytes in each
block) to format the device to. The default value is whatever is
currently reported by the block descriptor in a MODE SENSE com‐
mand. If the block size given by this option is different from
the current value then a MODE SELECT command is used to change
it prior to the FORMAT UNIT command being started (as recom‐
mended in the draft standard). Many SCSI disks have 512 byte
sectors by default and allow up to 16 bytes extra in a sector
(i.e. 528 byte sectors). If the given size in unacceptable with
the disk, most likely an "Invalid field in parameter list" mes‐
sage will appear in sense data (requires the use of '-v' to
decode sense data).
-v, --verbose
increase the level of verbosity, (i.e. debug output). "-vvv"
gives a lot more debug output.
-V, --version
print the version string and then exit.
-w, --wait
the default format action is to set the "IMMED" bit in the FOR‐
MAT UNIT command's (short) parameter header. If this option
(i.e. --wait) is given then the "IMMED" bit is not set. If
--wait is given the FORMAT UNIT command waits until the format
operation completes before returning its response. This can be
many hours on large disks. This utility sets a 15 hour timeout
on such a FORMAT UNIT command!
LISTS
The SBC-3 draft (revision 36) defines PLIST, CLIST, DLIST and GLIST in
section 4.13 on "Medium defects". Briefly, the PLIST is the "primary"
list of manufacturer detected defects, the CLIST ("certification" list)
contains those detected during the format operation, the DLIST is a
list of defects that can be given to the format operation. The GLIST is
the grown list which starts in the format process as CLIST+DLIST and
can "grow" later due to automatic reallocation (see the ARRE and AWRE
bits in the read-write error recovery mode page (see sdparm(8))) and
use of the SCSI REASSIGN BLOCKS command (see sg_reassign(8)).
The CMPLST bit (controlled by the --cmplst=0|1 option) determines
whether the existing GLIST, when the format operation is invoked, is
taken into account. The sg_format utility sets the FOV bit to zero
which causes DPRY=0, so the PLIST is taken into account, and DCRT=0, so
the CLIST is generated and used during the format process.
The sg_format utility does not permit a user to provide a defect list
(i.e. DLIST).
PROTECTION INFORMATION
Protection Information (PI) is additional information held with logical
blocks so that an application and/or host bus adapter can check the
correctness of those logical blocks. PI is placed in one or more pro‐
tection intervals beside each logical block. A protection interval con‐
tains 8 bytes made up of a 2 byte "logical block guard" (CRC), a 2 byte
"logical block application guard", and a 4 byte "logical block refer‐
ence tag". Devices with 512 byte logical block size typically have one
protection interval appended, making its logical block data 520 bytes
long. Devices with 4096 byte logical block size often have 8 protection
intervals spread across its logical block data for a total size of 4160
bytes. Note that for all other purposes the logical block size is con‐
sidered to be 512 and 4096 bytes respectively.
SBC-3 drafts have added several "protection types" to the PI introduced
in the SBC-2 standard. SBC-3 defines 4 protection types (types 0 to 3)
with protection type 0 meaning no PI is maintained. While a device may
support one or more protection types, it can only be formatted with 1
of the 4. To change a device's protection type, it must be re-format‐
ted. For more information see the Protection Information in section
4.22 of draft SBC-3 revision 36.
A device that supports PI information (i.e. supports one or more pro‐
tection types 1, 2 and 3) sets the "PROTECT" bit in its standard
INQUIRY response. It also sets the SPT field in the EXTENDED INQUIRY
VPD page response to indicate which protection types it supports. Given
PROTECT=1 then SPT=0 implies the device supports PI type 1 only, SPT=1
implies the device supports PI types 1 and 2, and various other
non-obvious mappings up to SPT=7 which implies protection types 1, 2
and 3 are supported. The current protection type of a disk can be found
in the "P_TYPE" and "PROT_EN" fields in the response of a READ CAPACITY
(16) command (e.g. with the 'sg_readcap --long' utility).
Given that a device supports a particular protection type, a user can
then choose to format that disk with that protection type by setting
the "FMTPINFO" and "Protection Field Usage" fields in the FORMAT UNIT
command. Those fields correspond to the --fmtpinfo=FPI and the
--pfu=PFU options in this utility. The list below shows the four pro‐
tection types followed by the options of this utility needed to select
them:
0 : --fmtpinfo=0 --pfu=0
1 : --fmtpinfo=2 --pfu=0
2 : --fmtpinfo=3 --pfu=0
3 : --fmtpinfo=3 --pfu=1
The default value of FPI (in --fmtpinfo=FPI) is 0 and the default value
of PFU (in --pfu=PFU) is 0. So if neither --fmtpinfo=FPI nor --pfu=PFU
are given then protection type 0 (i.e. no protection information) is
chosen.
NOTES
The SBC-2 standard states that the REQUEST SENSE command should be used
for obtaining progress indication when the format command is underway.
However, tests on a selection of disks shows that TEST UNIT READY com‐
mands yield progress indications (but not REQUEST SENSE commands). So
the current version of this utility defaults to using TEST UNIT READY
commands to poll the disk to find out the progress of the format. The
--poll=PT option has been added to control this.
When the --format option is given without the --wait option then the
SCSI FORMAT UNIT command is issued with the IMMED bit set which causes
the SCSI command to return after it has started the format operation.
The --early option will cause sg_format to exit at that point. Other‐
wise the DEVICE is polled every 60 seconds with TEST UNIT READY or
REQUEST SENSE commands until it reports an "all clear" (i.e. the format
operation has completed). Normally these polling commands will result
in a progress indicator (expressed as a percentage) being output to the
screen. If the user gets bored watching the progress report then
sg_format process can be terminated (e.g. with control-C) without
affecting the format operation which continues. However a target or
device reset (or a power cycle) will probably cause the device to
become "format corrupt".
When the --format and --wait options are both given then this utility
may take a long time to return. In this case care should be taken not
to send any other SCSI commands to the disk as it may not respond leav‐
ing those commands queued behind the active format command. This may
cause a timeout in the OS driver (in a lot shorter period than 15 hours
applicable to some format operations). This may result in the OS reset‐
ting the disk leaving the format operation incomplete. This may leave
the disk in a "format corrupt" state requiring another format to remedy
the situation.
When the block size (i.e. the number of bytes in each block) is changed
on a disk two SCSI commands must be sent: a MODE SELECT to change the
block size followed by a FORMAT command. If the MODE SELECT command
succeeds and the FORMAT fails then the disk may be in a state that the
draft standard calls "format corrupt". A block descriptor in a subse‐
quent MODE SENSE will report the requested new block size while a READ
CAPACITY command will report the existing (i.e. different) block size.
Alternatively the READ CAPACITY command may fail, reporting the device
is not ready, potentially requiring a format. The solution to this sit‐
uation is to do a format again (and this time the new block size does
not have to be given) or change the block size back to the original
size.
The SBC-2 standard states that the block count can be set back to the
manufacturer's maximum recommended value in a format or resize opera‐
tion. This can be done by placing an address of 0xffffffff (or the 64
bit equivalent) in the appropriate block descriptor field to a MODE
SELECT command. In signed (two's complement) arithmetic that value cor‐
responds to the manufacturer's maximum recommended value. To see
exactly which SCSI commands are being executed and parameters passed
add the "-vvv" option to the sg_format command line.
Short stroking is a technique to trade off capacity for performance.
Rotating disk performance is usually highest on the outer tracks (i.e.
lower logical block addresses) so by resizing or reformatting a disk to
a smaller capacity, average performance will usually be increased.
Other utilities may be useful in finding information associated with
formatting. These include sg_inq(8) to fetch standard INQUIRY informa‐
tion (e.g. the PROTECT bit) and to fetch the EXTENDED INQUIRY VPD page
(e.g. RTO and GRD_CHK bits). The sdparm(8) utility can be used to
access and potentially change the now obsolete format mode page.
scsiformat is another utility available for formatting SCSI disks with
Linux. It dates from 1997 (most recent update) and may be useful for
disks whose firmware is of that vintage.
The COUNT numeric argument may include a multiplicative suffix or be
given in hexadecimal. See the "NUMERIC ARGUMENTS" section in the
sg3_utils(8) man page.
The SCSI SANITIZE command was introduced in SBC-3 revision 27. It is
closely related to the ATA sanitize disk feature set and can be used to
remove all existing data from a disk. Sanitize is more likely to be
implemented on modern disks (including SSDs) than FORMAT UNIT's secu‐
rity initialization feature (see the --security option) and in some
cases much faster.
EXAMPLES
These examples use Linux device names. For suitable device names in
other supported Operating Systems see the sg3_utils(8) man page.
In the first example below simply find out the existing block count and
size derived from two sources: a block descriptor in a MODE SELECT com‐
mand response and from the response of a READ CAPACITY commands. No
changes are made:
# sg_format /dev/sdm
Now a simple format, leaving the block count and size as they were pre‐
viously. The FORMAT UNIT command is executed in IMMED mode and the
device is polled every 60 seconds to print out a progress indication:
# sg_format --format /dev/sdm
Now the same format, but waiting (passively) until the format operation
is complete:
# sg_format --format --wait /dev/sdm
Next is a format in which the block size is changed to 520 bytes and
the block count is set to the manufacturer's maximum value (for that
block size). Note, not all disks support changing the block size:
# sg_format --format --size=520 /dev/sdm
Now a resize operation so that only the first 0x10000 (65536) blocks on
a disk are accessible. The remaining blocks remain unaltered.
# sg_format --resize --count=0x10000 /dev/sdm
Now resize the disk back to its normal (maximum) block count:
# sg_format --resize --count=-1 /dev/sdm
One reason to format a SCSI disk is to add protection information.
First check which protection types are supported by a disk (by checking
the SPT field in the Extended inquiry VPD page together with the Pro‐
tect bit in the standard inquiry response):
# sg_vpd -p ei -l /dev/sdb
extended INQUIRY data VPD page:
ACTIVATE_MICROCODE=0
SPT=1 [protection types 1 and 2 supported]
....
Format with type 1 protection:
# sg_format --format --fmtpinfo=2 /dev/sdm
After a successful format with type 1 protection, READ CAPACITY(16)
should show something like this:
# sg_readcap -l /dev/sdm
Read Capacity results:
Protection: prot_en=1, p_type=0, p_i_exponent=0 [type 1 protec‐
tion]
Logical block provisioning: lbpme=0, lbprz=0
....
To format with type 3 protection:
# sg_format --format --fmtpinfo=3 --pfu=1 /dev/sdm
For the disk shown above this will probably fail because the Extended
inquiry VPD page showed only types 1 and 2 protection are supported.
EXIT STATUS
The exit status of sg_format is 0 when it is successful. Otherwise see
the sg3_utils(8) man page. Unless the --wait option is given, the exit
status may not reflect the success of otherwise of the format. Using
sg_turs(8) and sg_readcap(8) after the format operation may be wise.
AUTHORS
Written by Grant Grundler, James Bottomley and Douglas Gilbert.
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright © 2005-2014 Grant Grundler, James Bottomley and Douglas
Gilbert
This software is distributed under the GPL version 2. There is NO war‐
ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
POSE.
SEE ALSO
sg_turs(8), sg_requests(8), sg_inq(8), sg_modes(8), sg_vpd(8), sg_reas‐
sign(8), sg_readcap(8), sg3_utils(8), sg_sanitize(8) [all in
sg3_utils], sdparm(8), scsiformat (old), hdparm(8)
sg3_utils-1.38 March 2014 SG_FORMAT(8)
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