mkfs.xfs -l logdev=/dev/sdb1,size=100m /dev/sda1

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).

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. Sample configuration files can be found in /usr/share/xfsprogs/mkfs.

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.

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 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 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 create reverse mapping btrees when possible. 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.

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.

The data section must be at least 300MB in size.

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 block device, mkfs.xfs will automatically query the block device for appropriate sunit and swidth values if the block device and the filesystem size would be larger than 1GB.

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.

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.

Setting the value to 0 means that essentially all of the filesystem can become inode blocks (subject to possible inode32 mount option restrictions, see xfs(5) for details.)

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 enabled 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.

nrext64[=value]

Extend maximum values of inode data and attr fork extent counters from 2^31 - 1 and 2^15 - 1 to 2^48 - 1 and 2^32 - 1 respectively. If the value is omitted, 1 is assumed. This feature will be enabled when possible. This feature is only available for filesystems formatted with -m crc=1.

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.

The log must be at least 64MB in size. The log cannot be more than 2GB in size.

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.

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.

If the version=ci option is specified, the kernel will transform certain bytes in filenames before performing lookup-related operations. The byte sequence given to create a directory entry is persisted without alterations. The lookup transformations are defined as follows:

0x41-0x5a -> 0x61-0x7a

0xc0-0xd6 -> 0xe0-0xf6

0xd8-0xde -> 0xf8-0xfe

This transformation roughly corresponds to case insensitivity in ISO 8859-1. The transformations are not compatible with other encodings (e.g. UTF8). Do not enable this feature unless your entire environment has been coerced to ISO 8859-1. This feature is deprecated and will be removed in September 2030.

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.

[file=]protofile

The file= prefix is not required for this CLI argument for legacy reasons. If specified as a config file directive, the prefix is required.

If the optional 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:

* 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 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.

slashes_are_spaces=value

If set to 1, slashes ("/") in the first token of each line of the protofile are converted to spaces. This enables the creation of a filesystem containing filenames with spaces. By default, this is set to 0.

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.

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.