Provided by: xfsprogs_5.13.0-1ubuntu2_amd64 bug
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_section_options ] [ -n
naming_options ] [ -p protofile ] [ -q ] [ -r realtime_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 filesystem 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 may be used to specify the size of the sector or block. If the size of the
block or sector is not specified, the default sizes (block: 4KiB, sector: 512B) will be
used.
Many feature options allow an optional argument of 0 or 1, to explicitly disable or enable
the functionality.
OPTIONS
Options may be specified either on the command line or in a configuration file. Not all
command line options can be specified in configuration files; only the command line
options followed by a [section] label can be used in a configuration file.
Options that can be used in configuration files are grouped into related sections
containing multiple options. The command line options and configuration files use the
same option sections and grouping. Configuration file section names are listed in the
command line option sections below. Option names and values are the same for both command
line and configuration file specification.
Options specified are the combined set of command line parameters and configuration file
parameters. Duplicated options will result in a respecification error, regardless of the
location they were specified at.
This option specifies the files that mkfs configuration will be obtained from. The
valid configuration_file_option is:
options=name
The configuration options will be sourced from the file specified by
the name option string. This option can be use either an absolute or
relative path to the configuration file to be read.
Section Name: [block]
This option specifies the fundamental block size of the filesystem. 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).
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.
Section Name: [metadata]
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 feature, 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 architecture as some CPUs have hardware acceleration
of this algorithm. Typically the overhead of calculating and checking
the CRCs is not noticeable in normal operation.
By default, mkfs.xfs will enable metadata CRCs.
Formatting a filesystem without CRCs selects the V4 format, which is
deprecated and will be removed from upstream in September 2030.
Distributors may choose to withdraw support for the V4 format earlier
than this date. Several other options, noted below, are only tunable
on V4 formats, and will be removed along with the V4 format itself.
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 allocation
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 number 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 created 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 generate a random UUID.
rmapbt=value
This option enables the creation of a reverse-mapping 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 mappings 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 filesystems created with the (default) -m
crc=1 option set. When the option -m crc=0 is used, the reverse mapping
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 physical block, a reflink-
capable XFS filesystem removes the uniqueness requirement, allowing up
to four billion 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 logical-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, 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.
Section Name: [data]
These options specify the location, size, and other parameters of the data section
of the filesystem. The valid data_section_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 performance 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 suboption. The value is the
desired size of the allocation 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 automatically 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 regular
files and directories.
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 section. This suboption is
required if -d file[=1] is given. Otherwise, it is only needed if the
filesystem 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 suboption 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 suboption 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,
usually 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 logical 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 provides this information.
rtinherit=value
If value is set to 1, all inodes created by mkfs.xfs will be created
with the realtime flag set. The default is 0. Directories will pass
on this flag to newly created regular files and directories.
projinherit=value
All inodes created by mkfs.xfs will be assigned the project quota id
provided in value. Directories will pass on the project id to newly
created regular files and directories.
extszinherit=value
All inodes created by mkfs.xfs will have this value extent size hint
applied. The value must be provided in units of filesystem blocks.
Directories will pass on this hint to newly created regular files and
directories.
daxinherit=value
If value is set to 1, all inodes created by mkfs.xfs will be created
with the DAX flag set. The default is 0. Directories will pass on
this flag to newly created regular files and directories. By default,
mkfs.xfs will not enable DAX mode.
mkfs.xfs will not write to the device if it suspects that there is a filesystem or
partition table on the device already.
Section Name: [inode]
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:
directory 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 cannot 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 platforms) 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
significant 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 platforms).
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).
This option is only tunable on the deprecated V4 format.
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 algorithm 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.
This option is only tunable on the deprecated V4 format.
projid32bit[=value]
This is used to enable 32bit quota project identifiers. 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.)
This option is only tunable on the deprecated V4 format.
sparse[=value]
Enable sparse inode chunk allocation. The value is either 0 or 1, with
1 signifying that sparse allocation is enabled. If the value is
omitted, 1 is assumed. Sparse inode allocation is disabled by default.
This feature is only available for filesystems 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
allocations can fail with out of space errors under severe fragmented
free space conditions.
Section Name: [log]
These options specify the location, size, and other parameters of the log section
of the filesystem. The valid log_section_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.
This option is only tunable on the deprecated V4 format.
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 performance 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
automatically selected if the log su suboption is specified.
lazy-count=value
This changes the method of logging various persistent 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 persistent
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.
This option is only tunable on the deprecated V4 format.
Section Name: [naming]
These options specify the version and size parameters for the naming (directory)
area of the filesystem. The valid naming_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
directories 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 version 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-insensitive 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 functionality is always
enabled, and cannot be turned off.
In other words, this option is only tunable on the deprecated V4
format.
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 following 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 compatibility: two numeric values must appear at
this point for the proto file to be correctly parsed, but their values are
immaterial 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 specified 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:
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 regular file, a block special file, a character special
file, directory files, named pipes (first-in, first out files), and symbolic 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 specified, 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 numbers 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.
constructed; the -q flag suppresses this.
Section Name: [realtime]
These options specify the location, size, and other parameters of the real-time
section of the filesystem. The valid realtime_section_options are:
rtdev=device
This is used to specify the device which should contain 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
volume containing the section.
noalign
This option disables stripe size detection, enforcing a realtime device
with no stripe geometry.
Section Name: [sector]
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.
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.
file system.
Configuration File Format
The configuration file uses a basic INI format to specify sections and options within a
section. Section and option names are case sensitive. Section names must not contain
whitespace. Options are name-value pairs, ended by the first whitespace in the line.
Option names cannot contain whitespace. Full line comments can be added by starting a
line with a # symbol. If values contain whitespace, then it must be quoted.
The following example configuration file sets the block size to 4096 bytes, turns on
reverse mapping btrees and sets the inode size to 2048 bytes.
# Example mkfs.xfs configuration file
[block]
size=4k
[metadata]
rmapbt=1
[inode]
size=2048
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)