sg_format - format, format with preset, resize SCSI disk; format tape - man(8) - [phpMan]

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SG_FORMAT(8) SG3_UTILS SG_FORMAT(8)

NAME
sg_format - format, format with preset, resize SCSI disk; format tape

SYNOPSIS
sg_format [--cmplst={0|1}] [--count=COUNT] [--dcrt] [--dry-run] [--early] [--ffmt=FFMT]
[--fmtmaxlba-fmtpinfo=FPI] [--format] [--help] [--ip-def] [--long] [--mode=MP] [--pfu=PFU]
[--pie=PIE] [--pinfo] [--poll=PT] [--preset=ID] [--quick] [--resize] [--rto_req] [--security]
[--six] [--size=LB_SZ] [--tape=FM] [--timeout=SECS] [--verbose] [--verify] [--version]
[--wait] DEVICE

DESCRIPTION
Not all SCSI direct access devices need to be formatted and some have vendor specific format‐
ting procedures. SCSI disks with rotating media are probably the largest group that do sup‐
port 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 recommends. The manufac‐
turer's recommendation typically leaves aside a certain number of tracks, spread across the
media, for reassignment of blocks to logical block addresses during the life of the disk.

This utility issues one of three SCSI format commands: FORMAT UNIT, FORMAT MEDIUM or FORMAT
WITH PRESET. In the following description, unqualified sections will usually be referring to
the SCSI FORMAT UNIT command. Both FORMAT UNIT and FORMAT WITH PRESET apply to disks (or
disk-like devices). The FORMAT MEDIUM command is for tapes.

This utility can format modern SCSI disks and potentially change their block size (if permit‐
ted) and the block count (i.e. number of accessible blocks on the media also known as "resiz‐
ing"). 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 obso‐
leted 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. There is a Format Status log page
which reports on the previous successful format operation(s).

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 CAPACITY
command. The reason for this double check is to detect a "format corrupt" state (see the
NOTES section). This usage will not modify the disk.

When this utility is used with either --format, --preset=ID or --tape=FM, it will attempt to
format the given DEVICE. In the absence of the --quick option there is a 15 second pause dur‐
ing which time the user is invited thrice (5 seconds apart) to abort sg_format. This occurs
just prior the SCSI FORMAT UNIT, FORMAT WITH PRESET or FORMAT MEDIUM command being issued.
See the NOTES section for more information.

Protection information (PI) is optional and is made up of one or more protection intervals,
each made up of 8 bytes associated with a logical block. When PI is active each logical block
will have 1, 2, 4, 8, etc protection intervals (i.e. a power of two), interleaved with (and
following) the user data to which they refer. Four protection types are defined with protec‐
tion type 0 being no protection intervals. See the PROTECTION INFORMATION section below for
more information.

When the --tape=FM option is given then the SCSI FORMAT MEDIUM command is sent to the DEVICE.
FORMAT MEDIUM is defined in the SSC documents at T10 and prepares a volume for use. That may
include partitioning the medium. See the section below on TAPE for more information.

The FORMAT WITH PRESET was added in draft SBC-4 revision 18. A preset pattern, selected by
the PRESET IDENTIFIER field (--id=FWPID), is written to the disk. See the FORMAT PRESETS VPD
page (0xb8) for a list of available Format preset identifiers and their associated data.

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. If the value
is 0 then the existing GLIST (grown list) is taken into account. If the value is 1
then the existing GLIST is ignored. CMPLST defaults to 1 apart from when the
--ffmt=FFMT option's value is non-zero in which case CMPLST defaults to 0. See the
LISTS section below. In most cases this bit should be left at its default value.

-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". Certification verifies that blocks are usable during the
format process. Using this option may speed the format but --ffmt=FFMT, if available,
would probably be better. The default action of this utility (i.e. when this option is
not given) is to clear the DCRT bit thereby requesting "media certification" (also un‐
less another option needs it, the FOV bit will be cleared). When the DCRT bit is set,
the FOV bit must also be set hence sg_format does that.
If this option is given twice then certification is enabled by clearing the DCRT bit
and setting the FOV bit. Both these bits are found in the parameter list associated
with the FORMAT UNIT cdb.

-d, --dry-run
this option will parse the command line, do all the preparation but bypass the actual
FORMAT UNIT, FORMAT WITH PRESET or FORMAT MEDIUM command. Also if the options would
otherwise cause the logical block size to change, then the MODE SELECT command that
would do that is also bypassed when the dry run option is given.

-e, --early
during a format operation, The default action of this utility is to poll the disk
every 60 seconds (or every 10 seconds if FFMT is non-zero) 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.

-t, --ffmt=FFMT
FFMT (fast format) is placed in a field of the same name in the FORMAT UNIT cdb. The
field was introduced in SBC-4 revision 10. The default value is 0 which implies the
former action which is typically to overwrite all blocks on the DEVICE. That can take
a long time (e.g. with hard disks over 10 TB in size that can be days). With FFMT set
that time may be reduced to minutes or less. So it is worth trying if it is available.
FFMT has values 1 and 2 for fast format with 3 being reserved currently. These two
values include this description: "The device server initializes the medium ... without
overwriting the medium (i.e. resources for managing medium access are initialized and
the medium is not written)". The difference between 1 and 2 concerns read operations
on LBAs to which no data has been written to, after the fast format. When FFMT is 1
the read operation should return "unspecified logical block data" and complete without
error. When FFMT is 2 the read operation may yield check condition status with a sense
key set to hardware error, medium error or command aborted. See draft SBC-4 revision
16 section 4.34 for more details.

-b, --fmtmaxlba
This option is only active if it is given together with the --preset=ID option. If so
it sets the FMTMAXLBA field in the FORMAT WITH PRESET command.

-f, --fmtpinfo=FPI
sets the FMTPINFO field in the FORMAT UNIT cdb to a value between 0 and 3. The de‐
fault 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 revision 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 sec‐
tion below for more information.

-F, --format
issue one of the three SCSI "format" commands. In the absence of the --preset=ID and
--tape=FM options, the SCSI FORMAT UNIT command is issued. These commands will de‐
stroy all the data held on the media. This option is required to change the block
size of a disk. In the absence of the --quick option, the user is given a 15 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.
When used three times (or more) the preliminary MODE SENSE and SELECT commands are by‐
passed, leaving only the initial INQUIRY and FORMAT UNIT commands. This is for emer‐
gency use (e.g. when the MODE SENSE/SELECT commands are not working) and cannot change
the logical block size.
See NOTES section for implementation details and EXAMPLES section for typical use.

-h, --help
print out the usage information then exit.

-I, --ip-def
sets the default Initialization Pattern. Some disks (SSDs) use this to flag that a
format should fully provision (i.e. associate a physical block with every logical
block). The same disks (SSDs) might thin provision if this option is not given. If
this option is given then the --security option cannot be given. Also accepts --ip_def
for this option.

-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 op‐
tion 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 depending other parameters (e.g. when '--pie=PIE' is greater than zero).

-M, --mode=MP
MP is a mode page number (0 to 62 inclusive) that will be used for reading and perhaps
changing the device logical block size. The default is 1 which is the Read-Write Error
Recovery mode page.
Preferably the chosen (or default) mode page should be saveable (i.e. accept the SP
bit set in the MODE SELECT command used when the logical block size is being changed).
Recent version of this utility will retry a MODE SELECT if the SP=1 variant fails with
a sense key of ILLEGAL REQUEST. That retry will use the same MODE SELECT command but
with SP=0 .

-P, --pfu=PFU
sets the "Protection Field Usage" field in the parameter block associated with a FOR‐
MAT UNIT command to PFU. The default value is 0, the only other defined value cur‐
rently is 1. See the PROTECTION 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. PIE can only be non-zero with
protection types 2 and 3. The value of 0 is typical for 512 byte blocks; with 4096
byte blocks a value of 3 may be appropriate (i.e. 8 protection intervals interleaved
with 4096 bytes of user data). A device may not support any non-zero values. 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 --fmt‐
pinfo=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.

-E, --preset=ID
this option instructs this utility to issue a SCSI FORMAT WITH PRESET command. The
PRESET IDENTIFIER field in that cdb is set to ID. The IMMED field in that cdb is also
set unless the --wait option is also given, in which case it is cleared.

-Q, --quick
the default action (i.e. when the option is not given) is to give the user 15 seconds
to reconsider doing a format operation on the DEVICE. When this option is given that
step (i.e. the 15 second warning period) is skipped.

-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=LB_SZ
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 initializa‐
tion pattern descriptor within the parameter list. According to SBC-3 the default ini‐
tialization pattern "shall be written using a security erasure write technique". See
the NOTES section on the SCSI SANITIZE command. If this option is given then the
--ip_def option cannot be given.

-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=LB_SZ
where LB_SZ is the logical block size (i.e. number of user 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 command. If the block size given by this option is differ‐
ent from the current value then a MODE SELECT command is used to change it prior to
the FORMAT UNIT command being started (as recommended in the SBC standards). Some SCSI
disks have 512 byte logical blocks by default and allow an alternate logical block
size of 4096 bytes. If the given size in unacceptable to the disk, most likely an "In‐
valid field in parameter list" message will appear in sense data (requires the use of
'-v' to decode sense data).
Note that formatting a disk to add or remove protection information is not regarded as
a change to its logical block size so this option should not be used.

-T, --tape=FM
will send a FORMAT MEDIUM command to the DEVICE with its FORMAT field set to FM. This
option is used to prepare a tape (i.e. the "medium") in a tape drive for use. Values
for FM include 0 to do the "default" format; 1 to partition a volume and 2 to do a de‐
fault format then partition.

-m, --timeout=SECS
where SECS is the FORMAT UNIT, FORMAT WITH PRESET or FORMAT MEDIUM command timeout in
seconds. SECS will only be used if it exceeds the internal timeout which is 20 seconds
if the IMMED bit is set and 72000 seconds (20 hours) or higher if the IMMED bit is not
set. If the disk size exceeds 4 TB then the timeout value is increased to 144000 sec‐
onds (40 hours). And if it is greater than 8 TB then the timeout value is increased
to 288000 seconds (80 hours). If the timeout is exceeded then the operating system
will typically abort the command. Aborting a command may escalate to a LUN reset (or
worse). A timeout may also leave the disk or tape format operation incomplete. And
that may result in the disk or tape being in a "format corrupt" state requiring an‐
other format to remedy the situation. So for various reasons command timeouts are
best avoided.

-v, --verbose
increase the level of verbosity, (i.e. debug output). "-vvv" gives a lot more debug
output.

-y, --verify
set the VERIFY bit in the FORMAT MEDIUM cdb. The default is that the VERIFY bit is
clear. This option is only appropriate for tapes.

-V, --version
print the version string and then exit.

-w, --wait
the default format action is to set the "IMMED" bit in the FORMAT 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 then the FORMAT UNIT, FORMAT WITH PRESET or FORMAT
MEDIUM command waits until the format operation completes before returning its re‐
sponse. This can be many hours on large disks. See the --timeout=SECS option.
Alternatively this option may be useful when used together with --ffmt=FFMT (and FFMT
greater than 0) since the fast format may only be a matter of seconds.

LISTS
The SBC-3 draft (revision 20) defines PLIST, CLIST, DLIST and GLIST in section 4.10 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 sd‐
parm(8))) and use of the SCSI REASSIGN BLOCKS command (see sg_reassign(8)).

By the SBC-3 standard (following draft revision 36) the CLIST and DLIST had been removed,
leaving PLIST and GLIST. Only PLIST and GLIST are found in the SBC-4 drafts.

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 ap‐
plication and/or host bus adapter can check the correctness of those logical blocks. PI is
placed in one or more protection intervals interleaved in each logical block. Each protection
interval follows the user data to which it refers. A protection interval contains 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 reference tag". Devices with 512 byte logical block size typi‐
cally 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 logi‐
cal block size is considered to be 512 and 4096 bytes respectively.

The SBC-3 standard 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-formatted.
For more information see the Protection Information in section 4.21 of draft SBC-4 revision
16.

A device that supports PI information (i.e. supports one or more protection 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 PRO‐
TECT=1 then SPT=0 implies the device supports PI type 1 only, SPT=1 implies the device sup‐
ports PI types 1 and 2, and various other non-obvious mappings up to SPT=7 which implies pro‐
tection 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 protection 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
After a format that changes the logical block size or the number of logical blocks on a disk,
the operating system may need to be told to re-initialize its setting for that disk. In Linux
that can be done with:
echo 1 > /sys/block/sd{letter(s)}/device/rescan
where "letter(s)" will be between 'a' and 'zzz'. The lsscsi utility in Linux can be used to
check the various namings of a disk.

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 commands 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, --preset=ID or --tape=FM option is given without the --wait option then
the corresponding SCSI 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. Otherwise the DEVICE is polled every 60 seconds or every 10 seconds if
FFMT is non-zero. The poll is with TEST UNIT READY or REQUEST SENSE commands until one re‐
ports an "all clear" (i.e. the format operation has completed). Normally these polling com‐
mands 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. How‐
ever a target or device reset (or a power cycle) will probably cause the format to cease and
the DEVICE to become "format corrupt".

When the --format (--preset=ID or --tape) 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 leaving those commands queued behind the active
format command. This may cause a timeout in the OS driver (in a lot shorter period than 20
hours applicable to some format operations). This may result in the OS resetting the disk
leaving the format operation incomplete. This may leave the disk in a "format corrupt" state
requiring another format to remedy the situation. Modern SCSI devices should yield a "not
ready" sense key with an additional sense indicating a format is in progress. With older de‐
vices the user should take precautions that nothing attempts to access a device while it is
being formatted. Unmounting in mounted file systems on a DEVICE prior to calling this utility
is strongly advised.

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 standard calls "format corrupt". A block descriptor in a subsequent MODE SENSE will re‐
port the requested new block size while a READ CAPACITY command will report the existing
(i.e. previous) block size. Alternatively the READ CAPACITY command may fail, reporting the
device is not ready, potentially requiring a format. The solution to this situation 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 operation. This can be done by placing an address of
0xffffffff (or the 64 bit equivalent) in the appropriate block descriptor field to a MODE SE‐
LECT command. In signed (two's complement) arithmetic that value corresponds to '-1'. So a
--count=-1 causes the block count to be set back 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.

The FMTDATA field shown in the FORMAT UNIT cdb does not have a corresponding option in this
utility. When set in the cdb it indicates an additional parameter list will be sent to the
DEVICE along with the cdb. It is set as required, basically when any field in the parameter
list header is set.

Short stroking is a technique to trade off capacity for performance on hard disks. "Hard"
disk is often used to mean a storage device with spinning platters which contain the user
data. Solid State Disk (SSD) is the newer form of storage device that contains no moving
parts. Hard disk performance is usually highest on the outer tracks (usually the lower logi‐
cal 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 in‐
clude sg_inq(8) to fetch standard INQUIRY information (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. Sani‐
tize is more likely to be implemented on modern disks (including SSDs) than FORMAT UNIT's se‐
curity initialization feature (see the --security option) and in some cases much faster.

SSDs that support thin provisioning will typically unmap all logical blocks during a format.
The reason is to improve the SSD's endurance. Also thin provisioned formats typically com‐
plete faster than fully provisioned ones on the same disk (see the --ip_def option). In ei‐
ther case format operations on SSDs tend to be a lot faster than they are on hard disks with
spinning media.

TAPE
Tape system use a variant of the FORMAT UNIT command used on disks. Tape systems use the FOR‐
MAT MEDIUM command which is simpler with only three fields in the cdb typically used. Apart
from sharing the same opcode the cdbs of FORMAT UNIT and FORMAT MEDIUM are quite different.
FORMAT MEDIUM's fields are VERIFY, IMMED and FORMAT (with TRANSFER LENGTH always set to 0).
The VERIFY bit field is set with the --verify option. The IMMED bit is manipulated by the
--wait option in the same way it is for disks; one difference is that if the --poll=PT option
is not given then it defaults to PT of 1 which means the poll is done with REQUEST SENSE com‐
mands.

The argument given to the --tape=FM option is used to set the FORMAT field. FM can take val‐
ues from "-1" to "15" where "-1" (the default) means don't do a tape format; value "8" to
"15" are for vendor specific formats. The --early option may also be used to set the IMMED
bit and then exit this utility (rather than poll periodically until it is finished). In this
case the tape drive will still be busy doing the format for some time but, according to T10,
should still respond in full to the INQUIRY and REPORT LUNS commands. Other commands (includ‐
ing REQUEST SENSE) should yield a "not ready" sense key with an additional sense code of
"Logical unit not ready, format in progress". Additionally REQUEST SENSE should contain a
progress indication in its sense data.

When FM is 1 or 2 then the settings in the Medium partition mode page control the partition‐
ing. That mode page can be viewed and modified with the sdparm utility.

Prior to invoking this utility the tape may need to be positioned to the beginning of parti‐
tion 0. In Linux that can typically be done with the mt utility (e.g. 'mt -f /dev/st0
rewind').

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 command 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 previously. 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 chang‐
ing 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 accessi‐
ble. 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 protec‐
tion types are supported by a disk (by checking the SPT field in the Extended inquiry VPD
page together with the Protect 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 protection]
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.

Here are examples of using fast format (FFMT field in FORMAT UNIT cdb) to quickly switch be‐
tween 512 and 4096 byte logical block size. Assume disk starts with 4096 byte logical block
size and all important data has been backed up.

# sg_format --format --ffmt=1 --size=512 /dev/sdd

Now /dev/sdd should have 512 byte logical block size. And to switch it back:

# sg_format --format --ffmt=1 --size=4096 /dev/sdd

Since fast formats can be very quick (a matter of seconds) using the --wait option may be ap‐
propriate.

And to use the Format with preset command this invocation could be used:

# sg_format --preset=1 --fmtmaxlba /dev/sdd

The FORMAT PRESETS VPD page (0xb8) should be consulted to check that Preset identifier 0x1 is
there and has the expected format (i.e. "default host aware zoned block device model with 512
bytes of user data in each logical block"). That VPD page can be viewed with the sg_vpd
utility.

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 oth‐
erwise of the format. Using sg_turs(8) and sg_readcap(8) after the format operation may be
wise.

The Unix convention is that "no news is good news" but that can be a bit unnerving after an
operation like format, especially if it finishes quickly (i.e. before the first progress poll
is sent). Giving the --verbose option once should supply enough additional output to settle
those nerves.

AUTHORS
Written by Grant Grundler, James Bottomley and Douglas Gilbert.

REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT
Copyright © 2005-2020 Grant Grundler, James Bottomley and Douglas Gilbert
This software is distributed under the GPL version 2. There is NO warranty; not even for MER‐
CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

SEE ALSO
sg_turs(8), sg_requests(8), sg_inq(8), sg_modes(8), sg_vpd(8), sg_reassign(8), sg_readcap(8),
sg3_utils(8), sg_sanitize(8) [all in sg3_utils], lsscsi(8), mt(mt-st), sdparm(8), scsiformat
(old), hdparm(8)

sg3_utils-1.45 January 2020 SG_FORMAT(8)

man > sg_format(8)