mkfs.xfs(8) System Manager's Manual mkfs.xfs(8)
NAME
mkfs.xfs - construct an XFS filesystem
SYNOPSIS
mkfs.xfs [ -b block_size_options ] [ -m global_metadata_options ] [ -d
data_section_options ] [ -f ] [ -i inode_options ] [ -l log_sec-
tion_options ] [ -n naming_options ] [ -p protofile ] [ -q ] [ -r real-
time_section_options ] [ -s sector_size_options ] [ -L label ] [ -N ] [
-K ] device
mkfs.xfs -V
DESCRIPTION
mkfs.xfs constructs an XFS filesystem by writing on a special file
using the values found in the arguments of the command line. It is
invoked automatically by mkfs(8) when it is given the -t xfs option.
In its simplest (and most commonly used form), the size of the filesys-
tem is determined from the disk driver. As an example, to make a
filesystem with an internal log on the first partition on the first
SCSI disk, use:
mkfs.xfs /dev/sda1
The metadata log can be placed on another device to reduce the number
of disk seeks. To create a filesystem on the first partition on the
first SCSI disk with a 10MiB log located on the first partition on the
second SCSI disk, use:
mkfs.xfs -l logdev=/dev/sdb1,size=10m /dev/sda1
Each of the option elements in the argument list above can be given as
multiple comma-separated suboptions if multiple suboptions apply to the
same option. Equivalently, each main option can be given multiple
times with different suboptions. For example, -l internal,size=10m and
-l internal -l size=10m are equivalent.
In the descriptions below, sizes are given in sectors, bytes, blocks,
kilobytes, megabytes, gigabytes, etc. Sizes are treated as hexadecimal
if prefixed by 0x or 0X, octal if prefixed by 0, or decimal otherwise.
The following lists possible multiplication suffixes:
s - multiply by sector size (default = 512, see -s option
below).
b - multiply by filesystem block size (default = 4K, see -b
option below).
k - multiply by one kilobyte (1,024 bytes).
m - multiply by one megabyte (1,048,576 bytes).
g - multiply by one gigabyte (1,073,741,824 bytes).
t - multiply by one terabyte (1,099,511,627,776 bytes).
p - multiply by one petabyte (1,024 terabytes).
e - multiply by one exabyte (1,048,576 terabytes).
When specifying parameters in units of sectors or filesystem blocks,
the -s option or the -b option first needs to be added to the command
line. Failure to specify the size of the units will result in illegal
value errors when parameters are quantified in those units.
Many feature options allow an optional argument of 0 or 1, to explic-
itly disable or enable the functionality.
OPTIONS
-b block_size_options
This option specifies the fundamental block size of the filesys-
tem. The valid block_size_option is:
size=value
The filesystem block size is specified with a value
in bytes. The default value is 4096 bytes (4 KiB),
the minimum is 512, and the maximum is 65536 (64
KiB).
To specify any options on the command line in units
of filesystem blocks, this option must be specified
first so that the filesystem block size is applied
consistently to all options.
Although mkfs.xfs will accept any of these values
and create a valid filesystem, XFS on Linux can only
mount filesystems with pagesize or smaller blocks.
-m global_metadata_options
These options specify metadata format options that either apply
to the entire filesystem or aren't easily characterised by a
specific functionality group. The valid global_metadata_options
are:
bigtime=value
This option enables filesystems that can handle
inode timestamps from December 1901 to July 2486,
and quota timer expirations from January 1970 to
July 2486. The value is either 0 to disable the
feature, or 1 to enable large timestamps.
If this feature is not enabled, the filesystem can
only handle timestamps from December 1901 to January
2038, and quota timers from January 1970 to February
2106.
By default, mkfs.xfs will not enable this feature.
If the option -m crc=0 is used, the large timestamp
feature is not supported and is disabled.
crc=value
This is used to create a filesystem which maintains
and checks CRC information in all metadata objects
on disk. The value is either 0 to disable the fea-
ture, or 1 to enable the use of CRCs.
CRCs enable enhanced error detection due to hardware
issues, whilst the format changes also improves
crash recovery algorithms and the ability of various
tools to validate and repair metadata corruptions
when they are found. The CRC algorithm used is
CRC32c, so the overhead is dependent on CPU archi-
tecture as some CPUs have hardware acceleration of
this algorithm. Typically the overhead of calculat-
ing and checking the CRCs is not noticeable in nor-
mal operation.
By default, mkfs.xfs will enable metadata CRCs.
finobt=value
This option enables the use of a separate free inode
btree index in each allocation group. The value is
either 0 to disable the feature, or 1 to create a
free inode btree in each allocation group.
The free inode btree mirrors the existing allocated
inode btree index which indexes both used and free
inodes. The free inode btree does not index used
inodes, allowing faster, more consistent inode allo-
cation performance as filesystems age.
By default, mkfs.xfs will create free inode btrees
for filesystems created with the (default) -m crc=1
option set. When the option -m crc=0 is used, the
free inode btree feature is not supported and is
disabled.
inobtcount=value
This option causes the filesystem to record the num-
ber of blocks used by the inode btree and the free
inode btree. This can be used to reduce mount times
when the free inode btree is enabled.
By default, mkfs.xfs will not enable this option.
This feature is only available for filesystems cre-
ated with the (default) -m finobt=1 option set.
When the option -m finobt=0 is used, the inode btree
counter feature is not supported and is disabled.
uuid=value
Use the given value as the filesystem UUID for the
newly created filesystem. The default is to gener-
ate a random UUID.
rmapbt=value
This option enables the creation of a reverse-map-
ping btree index in each allocation group. The
value is either 0 to disable the feature, or 1 to
create the btree.
The reverse mapping btree maps filesystem blocks to
the owner of the filesystem block. Most of the map-
pings will be to an inode number and an offset,
though there will also be mappings to filesystem
metadata. This secondary metadata can be used to
validate the primary metadata or to pinpoint exactly
which data has been lost when a disk error occurs.
By default, mkfs.xfs will not create reverse mapping
btrees. This feature is only available for filesys-
tems created with the (default) -m crc=1 option set.
When the option -m crc=0 is used, the reverse map-
ping btree feature is not supported and is disabled.
reflink=value
This option enables the use of a separate reference
count btree index in each allocation group. The
value is either 0 to disable the feature, or 1 to
create a reference count btree in each allocation
group.
The reference count btree enables the sharing of
physical extents between the data forks of different
files, which is commonly known as "reflink". Unlike
traditional Unix filesystems which assume that every
inode and logical block pair map to a unique physi-
cal block, a reflink-capable XFS filesystem removes
the uniqueness requirement, allowing up to four bil-
lion arbitrary inode/logical block pairs to map to a
physical block. If a program tries to write to a
multiply-referenced block in a file, the write will
be redirected to a new block, and that file's logi-
cal-to-physical mapping will be changed to the new
block ("copy on write"). This feature enables the
creation of per-file snapshots and deduplication.
It is only available for the data forks of regular
files.
By default in Red Hat Enterprise Linux 8, mkfs.xfs
will create reference count btrees and therefore
will enable the reflink feature. This feature is
only available for filesystems created with the
(default) -m crc=1 option set. When the option -m
crc=0 is used, the reference count btree feature is
not supported and reflink is disabled.
Note: the filesystem DAX mount option ( -o dax ) is
incompatible with reflink-enabled XFS filesystems.
To use filesystem DAX with XFS, specify the -m
reflink=0 option to mkfs.xfs to disable the reflink
feature.
-d data_section_options
These options specify the location, size, and other parameters
of the data section of the filesystem. The valid data_sec-
tion_options are:
agcount=value
This is used to specify the number of allocation
groups. The data section of the filesystem is
divided into allocation groups to improve the per-
formance of XFS. More allocation groups imply that
more parallelism can be achieved when allocating
blocks and inodes. The minimum allocation group size
is 16 MiB; the maximum size is just under 1 TiB.
The data section of the filesystem is divided into
value allocation groups (default value is scaled
automatically based on the underlying device size).
agsize=value
This is an alternative to using the agcount subop-
tion. The value is the desired size of the alloca-
tion group expressed in bytes (usually using the m
or g suffixes). This value must be a multiple of
the filesystem block size, and must be at least
16MiB, and no more than 1TiB, and may be automati-
cally adjusted to properly align with the stripe
geometry. The agcount and agsize suboptions are
mutually exclusive.
cowextsize=value
Set the copy-on-write extent size hint on all inodes
created by mkfs.xfs. The value must be provided in
units of filesystem blocks. If the value is zero,
the default value (currently 32 blocks) will be
used. Directories will pass on this hint to newly
created children.
name=value
This can be used to specify the name of the special
file containing the filesystem. In this case, the
log section must be specified as internal (with a
size, see the -l option below) and there can be no
real-time section.
file[=value]
This is used to specify that the file given by the
name suboption is a regular file. The value is
either 0 or 1, with 1 signifying that the file is
regular. This suboption is used only to make a
filesystem image. If the value is omitted then 1 is
assumed.
size=value
This is used to specify the size of the data sec-
tion. This suboption is required if -d file[=1] is
given. Otherwise, it is only needed if the filesys-
tem should occupy less space than the size of the
special file.
sunit=value
This is used to specify the stripe unit for a RAID
device or a logical volume. The value has to be
specified in 512-byte block units. Use the su subop-
tion to specify the stripe unit size in bytes. This
suboption ensures that data allocations will be
stripe unit aligned when the current end of file is
being extended and the file size is larger than
512KiB. Also inode allocations and the internal log
will be stripe unit aligned.
su=value
This is an alternative to using sunit. The su sub-
option is used to specify the stripe unit for a RAID
device or a striped logical volume. The value has to
be specified in bytes, (usually using the m or g
suffixes). This value must be a multiple of the
filesystem block size.
swidth=value
This is used to specify the stripe width for a RAID
device or a striped logical volume. The value has to
be specified in 512-byte block units. Use the sw
suboption to specify the stripe width size in bytes.
This suboption is required if -d sunit has been
specified and it has to be a multiple of the -d
sunit suboption.
sw=value
suboption is an alternative to using swidth. The sw
suboption is used to specify the stripe width for a
RAID device or striped logical volume. The value is
expressed as a multiplier of the stripe unit, usu-
ally the same as the number of stripe members in the
logical volume configuration, or data disks in a
RAID device.
When a filesystem is created on a logical volume
device, mkfs.xfs will automatically query the logi-
cal volume for appropriate sunit and swidth values.
noalign
This option disables automatic geometry detection
and creates the filesystem without stripe geometry
alignment even if the underlying storage device pro-
vides this information.
rtinherit=value
If set, all inodes created by mkfs.xfs will be cre-
ated with the realtime flag set. Directories will
pass on this flag to newly created children.
projinherit=value
All inodes created by mkfs.xfs will be assigned this
project quota id. Directories will pass on the
project id to newly created children.
extszinherit=value
All inodes created by mkfs.xfs will have this extent
size hint applied. The value must be provided in
units of filesystem blocks. Directories will pass
on this hint to newly created children.
-f Force overwrite when an existing filesystem is detected on the
device. By default, mkfs.xfs will not write to the device if it
suspects that there is a filesystem or partition table on the
device already.
-i inode_options
This option specifies the inode size of the filesystem, and
other inode allocation parameters. The XFS inode contains a
fixed-size part and a variable-size part. The variable-size
part, whose size is affected by this option, can contain: direc-
tory data, for small directories; attribute data, for small
attribute sets; symbolic link data, for small symbolic links;
the extent list for the file, for files with a small number of
extents; and the root of a tree describing the location of
extents for the file, for files with a large number of extents.
The valid inode_options are:
size=value | perblock=value
The inode size is specified either as a value in
bytes with size= or as the number fitting in a
filesystem block with perblock=. The minimum (and
default) value is 256 bytes without crc, 512 bytes
with crc enabled. The maximum value is 2048 (2 KiB)
subject to the restriction that the inode size can-
not exceed one half of the filesystem block size.
XFS uses 64-bit inode numbers internally; however,
the number of significant bits in an inode number is
affected by filesystem geometry. In practice,
filesystem size and inode size are the predominant
factors. The Linux kernel (on 32 bit hardware plat-
forms) and most applications cannot currently handle
inode numbers greater than 32 significant bits, so
if no inode size is given on the command line,
mkfs.xfs will attempt to choose a size such that
inode numbers will be < 32 bits. If an inode size
is specified, or if a filesystem is sufficiently
large, mkfs.xfs will warn if this will create inode
numbers > 32 significant bits.
maxpct=value
This specifies the maximum percentage of space in
the filesystem that can be allocated to inodes. The
default value is 25% for filesystems under 1TB, 5%
for filesystems under 50TB and 1% for filesystems
over 50TB.
In the default inode allocation mode, inode blocks
are chosen such that inode numbers will not exceed
32 bits, which restricts the inode blocks to the
lower portion of the filesystem. The data block
allocator will avoid these low blocks to accommodate
the specified maxpct, so a high value may result in
a filesystem with nothing but inodes in a signifi-
cant portion of the lower blocks of the filesystem.
(This restriction is not present when the filesystem
is mounted with the inode64 option on 64-bit plat-
forms).
Setting the value to 0 means that essentially all of
the filesystem can become inode blocks, subject to
inode32 restrictions.
This value can be modified with xfs_growfs(8).
align[=value]
This is used to specify that inode allocation is or
is not aligned. The value is either 0 or 1, with 1
signifying that inodes are allocated aligned. If
the value is omitted, 1 is assumed. The default is
that inodes are aligned. Aligned inode access is
normally more efficient than unaligned access;
alignment must be established at the time the
filesystem is created, since inodes are allocated at
that time. This option can be used to turn off
inode alignment when the filesystem needs to be
mountable by a version of IRIX that does not have
the inode alignment feature (any release of IRIX
before 6.2, and IRIX 6.2 without XFS patches).
attr=value
This is used to specify the version of extended
attribute inline allocation policy to be used. By
default, this is 2, which uses an efficient algo-
rithm for managing the available inline inode space
between attribute and extent data.
The previous version 1, which has fixed regions for
attribute and extent data, is kept for backwards
compatibility with kernels older than version
2.6.16.
projid32bit[=value]
This is used to enable 32bit quota project identi-
fiers. The value is either 0 or 1, with 1 signifying
that 32bit projid are to be enabled. If the value
is omitted, 1 is assumed. (This default changed in
release version 3.2.0.)
sparse[=value]
Enable sparse inode chunk allocation. The value is
either 0 or 1, with 1 signifying that sparse alloca-
tion is enabled. If the value is omitted, 1 is
assumed. Sparse inode allocation is enabled by
default. This feature is only available for filesys-
tems formatted with -m crc=1.
When enabled, sparse inode allocation allows the
filesystem to allocate smaller than the standard
64-inode chunk when free space is severely limited.
This feature is useful for filesystems that might
fragment free space over time such that no free
extents are large enough to accommodate a chunk of
64 inodes. Without this feature enabled, inode allo-
cations can fail with out of space errors under
severe fragmented free space conditions.
-l log_section_options
These options specify the location, size, and other parameters
of the log section of the filesystem. The valid log_sec-
tion_options are:
agnum=value
If the log is internal, allocate it in this AG.
internal[=value]
This is used to specify that the log section is a
piece of the data section instead of being another
device or logical volume. The value is either 0 or
1, with 1 signifying that the log is internal. If
the value is omitted, 1 is assumed.
logdev=device
This is used to specify that the log section should
reside on the device separate from the data section.
The internal=1 and logdev options are mutually
exclusive.
size=value
This is used to specify the size of the log section.
If the log is contained within the data section and
size isn't specified, mkfs.xfs will try to select a
suitable log size depending on the size of the
filesystem. The actual logsize depends on the
filesystem block size and the directory block size.
Otherwise, the size suboption is only needed if the
log section of the filesystem should occupy less
space than the size of the special file. The value
is specified in bytes or blocks, with a b suffix
meaning multiplication by the filesystem block size,
as described above. The overriding minimum value for
size is 512 blocks. With some combinations of
filesystem block size, inode size, and directory
block size, the minimum log size is larger than 512
blocks.
version=value
This specifies the version of the log. The current
default is 2, which allows for larger log buffer
sizes, as well as supporting stripe-aligned log
writes (see the sunit and su options, below).
The previous version 1, which is limited to 32k log
buffers and does not support stripe-aligned writes,
is kept for backwards compatibility with very old
2.4 kernels.
sunit=value
This specifies the alignment to be used for log
writes. The value has to be specified in 512-byte
block units. Use the su suboption to specify the log
stripe unit size in bytes. Log writes will be
aligned on this boundary, and rounded up to this
boundary. This gives major improvements in perfor-
mance on some configurations such as software RAID5
when the sunit is specified as the filesystem block
size. The equivalent byte value must be a multiple
of the filesystem block size. Version 2 logs are
automatically selected if the log sunit suboption is
specified.
The su suboption is an alternative to using sunit.
su=value
This is used to specify the log stripe. The value
has to be specified in bytes, (usually using the s
or b suffixes). This value must be a multiple of the
filesystem block size. Version 2 logs are automati-
cally selected if the log su suboption is specified.
lazy-count=value
This changes the method of logging various persis-
tent counters in the superblock. Under metadata
intensive workloads, these counters are updated and
logged frequently enough that the superblock updates
become a serialization point in the filesystem. The
value can be either 0 or 1.
With lazy-count=1, the superblock is not modified or
logged on every change of the persistent counters.
Instead, enough information is kept in other parts
of the filesystem to be able to maintain the persis-
tent counter values without needed to keep them in
the superblock. This gives significant improvements
in performance on some configurations. The default
value is 1 (on) so you must specify lazy-count=0 if
you want to disable this feature for older kernels
which don't support it.
-n naming_options
These options specify the version and size parameters for the
naming (directory) area of the filesystem. The valid nam-
ing_options are:
size=value
The directory block size is specified with a value
in bytes. The block size must be a power of 2 and
cannot be less than the filesystem block size. The
default size value for version 2 directories is 4096
bytes (4 KiB), unless the filesystem block size is
larger than 4096, in which case the default value is
the filesystem block size. For version 1 directo-
ries the block size is the same as the filesystem
block size.
version=value
The naming (directory) version value can be either 2
or 'ci', defaulting to 2 if unspecified. With ver-
sion 2 directories, the directory block size can be
any power of 2 size from the filesystem block size
up to 65536.
The version=ci option enables ASCII only case-insen-
sitive filename lookup and version 2 directories.
Filenames are case-preserving, that is, the names
are stored in directories using the case they were
created with.
Note: Version 1 directories are not supported.
ftype=value
This feature allows the inode type to be stored in
the directory structure so that the readdir(3) and
getdents(2) do not need to look up the inode to
determine the inode type.
The value is either 0 or 1, with 1 signifying that
filetype information will be stored in the directory
structure. The default value is 1.
When CRCs are enabled (the default), the ftype func-
tionality is always enabled, and cannot be turned
off.
-p protofile
If the optional -p protofile argument is given, mkfs.xfs uses
protofile as a prototype file and takes its directions from that
file. The blocks and inodes specifiers in the protofile are
provided for backwards compatibility, but are otherwise unused.
The syntax of the protofile is defined by a number of tokens
separated by spaces or newlines. Note that the line numbers are
not part of the syntax but are meant to help you in the follow-
ing discussion of the file contents.
1 /stand/diskboot
2 4872 110
3 d--777 3 1
4 usr d--777 3 1
5 sh ---755 3 1 /bin/sh
6 ken d--755 6 1
7 $
8 b0 b--644 3 1 0 0
9 c0 c--644 3 1 0 0
10 fifo p--644 3 1
11 slink l--644 3 1 /a/symbolic/link
12 : This is a comment line
13 $
14 $
Line 1 is a dummy string. (It was formerly the bootfilename.)
It is present for backward compatibility; boot blocks are not
used on SGI systems.
Note that some string of characters must be present as the first
line of the proto file to cause it to be parsed correctly; the
value of this string is immaterial since it is ignored.
Line 2 contains two numeric values (formerly the numbers of
blocks and inodes). These are also merely for backward compati-
bility: two numeric values must appear at this point for the
proto file to be correctly parsed, but their values are immate-
rial since they are ignored.
The lines 3 through 11 specify the files and directories you
want to include in this filesystem. Line 3 defines the root
directory. Other directories and files that you want in the
filesystem are indicated by lines 4 through 6 and lines 8
through 10. Line 11 contains symbolic link syntax.
Notice the dollar sign ($) syntax on line 7. This syntax directs
the mkfs.xfs command to terminate the branch of the filesystem
it is currently on and then continue from the directory speci-
fied by the next line, in this case line 8. It must be the last
character on a line. The colon on line 12 introduces a comment;
all characters up until the following newline are ignored. Note
that this means you cannot have a file in a prototype file whose
name contains a colon. The $ on lines 13 and 14 end the
process, since no additional specifications follow.
File specifications provide the following:
* file mode
* user ID
* group ID
* the file's beginning contents
A 6-character string defines the mode for a file. The first
character of this string defines the file type. The character
range for this first character is -bcdpl. A file may be a regu-
lar file, a block special file, a character special file, direc-
tory files, named pipes (first-in, first out files), and sym-
bolic links. The second character of the mode string is used to
specify setuserID mode, in which case it is u. If setuserID
mode is not specified, the second character is -. The third
character of the mode string is used to specify the setgroupID
mode, in which case it is g. If setgroupID mode is not speci-
fied, the third character is -. The remaining characters of the
mode string are a three digit octal number. This octal number
defines the owner, group, and other read, write, and execute
permissions for the file, respectively. For more information on
file permissions, see the chmod(1) command.
Following the mode character string are two decimal number
tokens that specify the user and group IDs of the file's owner.
In a regular file, the next token specifies the pathname from
which the contents and size of the file are copied. In a block
or character special file, the next token are two decimal num-
bers that specify the major and minor device numbers. When a
file is a symbolic link, the next token specifies the contents
of the link.
When the file is a directory, the mkfs.xfs command creates the
entries dot (.) and dot-dot (..) and then reads the list of
names and file specifications in a recursive manner for all of
the entries in the directory. A scan of the protofile is always
terminated with the dollar ( $ ) token.
-q Quiet option. Normally mkfs.xfs prints the parameters of the
filesystem to be constructed; the -q flag suppresses this.
-r realtime_section_options
These options specify the location, size, and other parameters
of the real-time section of the filesystem. The valid real-
time_section_options are:
rtdev=device
This is used to specify the device which should con-
tain the real-time section of the filesystem. The
suboption value is the name of a block device.
extsize=value
This is used to specify the size of the blocks in
the real-time section of the filesystem. This value
must be a multiple of the filesystem block size. The
minimum allowed size is the filesystem block size or
4 KiB (whichever is larger); the default size is the
stripe width for striped volumes or 64 KiB for non-
striped volumes; the maximum allowed size is 1 GiB.
The real-time extent size should be carefully chosen
to match the parameters of the physical media used.
size=value
This is used to specify the size of the real-time
section. This suboption is only needed if the real-
time section of the filesystem should occupy less
space than the size of the partition or logical vol-
ume containing the section.
noalign
This option disables stripe size detection, enforc-
ing a realtime device with no stripe geometry.
-s sector_size_options
This option specifies the fundamental sector size of the
filesystem. The valid sector_size_option is:
size=value
The sector size is specified with a value in bytes.
The default sector_size is 512 bytes. The minimum
value for sector size is 512; the maximum is 32768
(32 KiB). The sector_size must be a power of 2 size
and cannot be made larger than the filesystem block
size.
To specify any options on the command line in units
of sectors, this option must be specified first so
that the sector size is applied consistently to all
options.
-L label
Set the filesystem label. XFS filesystem labels can be at most
12 characters long; if label is longer than 12 characters,
mkfs.xfs will not proceed with creating the filesystem. Refer
to the mount(8) and xfs_admin(8) manual entries for additional
information.
-N Causes the file system parameters to be printed out without
really creating the file system.
-K Do not attempt to discard blocks at mkfs time.
-V Prints the version number and exits.
SEE ALSO
xfs(5), mkfs(8), mount(8), xfs_info(8), xfs_admin(8).
BUGS
With a prototype file, it is not possible to specify hard links.
mkfs.xfs(8)
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