# mkfs.btrfs

## NAME



           mkfs.btrfs - create a btrfs filesystem
    


## SYNOPSIS



           **mkfs.btrfs**[options] _< device>_ [_< device>_...]
    


## DESCRIPTION



           **mkfs.btrfs** is used to create the btrfs filesystem on a single or
           multiple devices. _< device>_ is typically a block device but can be
           a file-backed image as well. Multiple devices are grouped by UUID
           of the filesystem.
    
           Before mounting such filesystem, the kernel module must know all
           the devices either via preceding execution of **btrfs device scan** or
           using the **device** mount option. See section **MULTIPLE DEVICES** for
           more details.
    
           The default block group profiles for data and metadata depend on
           number of devices and possibly other factors. It’s recommended to
           use specific profiles but the defaults should be OK and allowing
           future conversions to other profiles. Please see options _-d_ and _-m_
           for further detals and btrfs-balance(8) for the profile conversion
           post mkfs.
    


## OPTIONS



           **-b|--byte-count** _< size>_
               Specify the size of the filesystem. If this option is not
               used, then mkfs.btrfs uses the entire device space for the
               filesystem.
    
           **--csum** _< type>_, **--checksum** _< type>_
               Specify the checksum algorithm. Default is _crc32c_. Valid
               values are _crc32c_ , _xxhash_ , _sha256_ or _blake2_. To mount such
               filesystem kernel must support the checksums as well. See
               _CHECKSUM ALGORITHMS_ in **btrfs**(5).
    
           **-d|--data** _< profile>_
               Specify the profile for the data block groups. Valid values
               are _raid0_ , _raid1_ , _raid1c3_ , _raid1c4_ , _raid5_ , _raid6_ , _raid10_ or
               _single_ or _dup_ (case does not matter).
    
               See _DUP PROFILES ON A SINGLE DEVICE_ for more details.
    
               On multiple devices, the default was _raid0_ until version 5.7,
               while it is _single_ since version 5.8. You can still select
               raid0 manually, but it was not suitable as default.
    
           **-m|--metadata** _< profile>_
               Specify the profile for the metadata block groups. Valid
               values are _raid0_ , _raid1_ , _raid1c3_ , _raid1c4_ , _raid5_ , _raid6_ ,
               _raid10_ , _single_ or _dup_ (case does not matter).
    
               Default on a single device filesystem is _DUP_ and is
               recommended for metadata in general. The duplication might not
               be necessary in some use cases and it’s up to the user to
               changed that at mkfs time or later. This depends on hardware
               that could potentially deduplicate the blocks again but this
               cannot be detected at mkfs time.
    
                   **NOTE**
                   Up to version 5.14 there was a detection of a SSD device
                   (more precisely if it’s a rotational device, determined by
                   the contents of file **/sys/block/DEV/queue/rotational**) that
                   used to select _single_. This has changed in version 5.15 to
                   be always _dup_.
    
                   Note that the rotational status can be arbitrarily set by
                   the underlying block device driver and may not reflect the
                   true status (network block device, memory-backed SCSI
                   devices, real block device behind some additional device
                   mapper layer, etc). It’s recommended to always set the
                   options _--data/--metadata_ to avoid confusion and
                   unexpected results.
    
                   See _DUP PROFILES ON A SINGLE DEVICE_ for more details.
               On multiple devices the default is _raid1_.
    
           **-M|--mixed**
               Normally the data and metadata block groups are isolated. The
               _mixed_ mode will remove the isolation and store both types in
               the same block group type. This helps to utilize the free
               space regardless of the purpose and is suitable for small
               devices. The separate allocation of block groups leads to a
               situation where the space is reserved for the other block
               group type, is not available for allocation and can lead to
               ENOSPC state.
    
               The recommended size for the mixed mode is for filesystems
               less than 1GiB. The soft recommendation is to use it for
               filesystems smaller than 5GiB. The mixed mode may lead to
               degraded performance on larger filesystems, but is otherwise
               usable, even on multiple devices.
    
               The _nodesize_ and _sectorsize_ must be equal, and the block group
               types must match.
    
                   **Note**
                   versions up to 4.2.x forced the mixed mode for devices
                   smaller than 1GiB. This has been removed in 4.3+ as it
                   caused some usability issues.
    
           **-l|--leafsize** _< size>_
               Alias for --nodesize. Deprecated.
    
           **-n|--nodesize** _< size>_
               Specify the nodesize, the tree block size in which btrfs
               stores metadata. The default value is 16KiB (16384) or the
               page size, whichever is bigger. Must be a multiple of the
               sectorsize and a power of 2, but not larger than 64KiB
               (65536). Leafsize always equals nodesize and the options are
               aliases.
    
               Smaller node size increases fragmentation but leads to taller
               b-trees which in turn leads to lower locking contention.
               Higher node sizes give better packing and less fragmentation
               at the cost of more expensive memory operations while updating
               the metadata blocks.
    
                   **Note**
                   versions up to 3.11 set the nodesize to 4k.
    
           **-s|--sectorsize** _< size>_
               Specify the sectorsize, the minimum data block allocation
               unit.
    
               The default value is the page size and is autodetected. If the
               sectorsize differs from the page size, the created filesystem
               may not be mountable by the running kernel. Therefore it is
               not recommended to use this option unless you are going to
               mount it on a system with the appropriate page size.
    
           **-L|--label** _< string>_
               Specify a label for the filesystem. The _string_ should be less
               than 256 bytes and must not contain newline characters.
    
           **-K|--nodiscard**
               Do not perform whole device TRIM operation on devices that are
               capable of that. This does not affect discard/trim operation
               when the filesystem is mounted. Please see the mount option
               _discard_ for that in **btrfs**(5).
    
           **-r|--rootdir** _< rootdir>_
               Populate the toplevel subvolume with files from _rootdir_. This
               does not require root permissions to write the new files or to
               mount the filesystem.
    
                   **Note**
                   This option may enlarge the image or file to ensure it’s
                   big enough to contain the files from _rootdir_. Since
                   version 4.14.1 the filesystem size is not minimized.
                   Please see option _--shrink_ if you need that functionality.
    
           **--shrink**
               Shrink the filesystem to its minimal size, only works with
               _--rootdir_ option.
    
               If the destination block device is a regular file, this option
               will also truncate the file to the minimal size. Otherwise it
               will reduce the filesystem available space. Extra space will
               not be usable unless the filesystem is mounted and resized
               using _btrfs filesystem resize_.
    
                   **Note**
                   prior to version 4.14.1, the shrinking was done
                   automatically.
    
           **-O|--features** _< feature1>_**[,**_< feature2>_**...]**
               A list of filesystem features turned on at mkfs time. Not all
               features are supported by old kernels. To disable a feature,
               prefix it with _^_.
    
               See section **FILESYSTEM FEATURES** for more details. To see all
               available features that mkfs.btrfs supports run:
    
               **mkfs.btrfs -O list-all**
    
           **-R|--runtime-features** _< feature1>_**[,**_< feature2>_**...]**
               A list of features that be can enabled at mkfs time, otherwise
               would have to be turned on a mounted filesystem. Although no
               runtime feature is enabled by default, to disable a feature,
               prefix it with _^_.
    
               See section **RUNTIME FEATURES** for more details. To see all
               available runtime features that mkfs.btrfs supports run:
    
               **mkfs.btrfs -R list-all**
    
           **-f|--force**
               Forcibly overwrite the block devices when an existing
               filesystem is detected. By default, mkfs.btrfs will utilize
               _libblkid_ to check for any known filesystem on the devices.
               Alternatively you can use the **wipefs** utility to clear the
               devices.
    
           **-q|--quiet**
               Print only error or warning messages. Options --features or
               --help are unaffected. Resets any previous effects of
               _--verbose_.
    
           **-U|--uuid** _< UUID>_
               Create the filesystem with the given _UUID_. The UUID must not
               exist on any filesystem currently present.
    
           **-v|--verbose**
               Increase verbosity level, default is 1.
    
           **-V|--version**
               Print the **mkfs.btrfs** version and exit.
    
           **--help**
               Print help.
    


## SIZE UNITS



           The default unit is _byte_. All size parameters accept suffixes in
           the 1024 base. The recognized suffixes are: _k_ , _m_ , _g_ , _t_ , _p_ , _e_ , both
           uppercase and lowercase.
    


## MULTIPLE DEVICES



           Before mounting a multiple device filesystem, the kernel module
           must know the association of the block devices that are attached
           to the filesystem UUID.
    
           There is typically no action needed from the user. On a system
           that utilizes a udev-like daemon, any new block device is
           automatically registered. The rules call **btrfs device scan**.
    
           The same command can be used to trigger the device scanning if the
           btrfs kernel module is reloaded (naturally all previous
           information about the device registration is lost).
    
           Another possibility is to use the mount options **device** to specify
           the list of devices to scan at the time of mount.
    
               # mount -o device=/dev/sdb,device=/dev/sdc /dev/sda /mnt
    
               **Note**
    
               that this means only scanning, if the devices do not exist in
               the system, mount will fail anyway. This can happen on systems
               without initramfs/initrd and root partition created with
               RAID1/10/5/6 profiles. The mount action can happen before all
               block devices are discovered. The waiting is usually done on
               the initramfs/initrd systems.
    
           RAID5/6 has known problems and should not be used in production.
    


## FILESYSTEM FEATURES



           Features that can be enabled during creation time. See also
           **btrfs**(5) section _FILESYSTEM FEATURES_.
    
           **mixed-bg**
               (kernel support since 2.6.37)
    
               mixed data and metadata block groups, also set by option
               _--mixed_
    
           **extref**
               (default since btrfs-progs 3.12, kernel support since 3.7)
    
               increased hardlink limit per file in a directory to 65536,
               older kernels supported a varying number of hardlinks
               depending on the sum of all file name sizes that can be stored
               into one metadata block
    
           **raid56**
               (kernel support since 3.9)
    
               extended format for RAID5/6, also enabled if raid5 or raid6
               block groups are selected
    
           **skinny-metadata**
               (default since btrfs-progs 3.18, kernel support since 3.10)
    
               reduced-size metadata for extent references, saves a few
               percent of metadata
    
           **no-holes**
               (default since btrfs-progs 5.15, kernel support since 3.14)
    
               improved representation of file extents where holes are not
               explicitly stored as an extent, saves a few percent of
               metadata if sparse files are used
    
           **zoned**
               (kernel support since 5.12)
    
               zoned mode, data allocation and write friendly to
               zoned/SMR/ZBC/ZNS devices, see _ZONED MODE_ in **btrfs**(5), the
               mode is automatically selected when a zoned device is detected
    


## RUNTIME FEATURES



           Features that are typically enabled on a mounted filesystem, eg.
           by a mount option or by an ioctl. Some of them can be enabled
           early, at mkfs time. This applies to features that need to be
           enabled once and then the status is permanent, this does not
           replace mount options.
    
           **quota**
               (kernel support since 3.4)
    
               Enable quota support (qgroups). The qgroup accounting will be
               consistent, can be used together with _--rootdir_. See also
               btrfs-quota(8).
    
           **free-space-tree**
               (default since btrfs-progs 5.15, kernel support since 4.5)
    
               Enable the free space tree (mount option space_cache=v2) for
               persisting the free space cache.
    


## BLOCK GROUPS, CHUNKS, RAID



           The highlevel organizational units of a filesystem are block
           groups of three types: data, metadata and system.
    
           **DATA**
               store data blocks and nothing else
    
           **METADATA**
               store internal metadata in b-trees, can store file data if
               they fit into the inline limit
    
           **SYSTEM**
               store structures that describe the mapping between the
               physical devices and the linear logical space representing the
               filesystem
    
           Other terms commonly used:
    
           **block group** , **chunk**
               a logical range of space of a given profile, stores data,
               metadata or both; sometimes the terms are used interchangeably
    
               A typical size of metadata block group is 256MiB (filesystem
               smaller than 50GiB) and 1GiB (larger than 50GiB), for data
               it’s 1GiB. The system block group size is a few megabytes.
    
           **RAID**
               a block group profile type that utilizes RAID-like features on
               multiple devices: striping, mirroring, parity
    
           **profile**
               when used in connection with block groups refers to the
               allocation strategy and constraints, see the section _PROFILES_
               for more details
    


## PROFILES



           There are the following block group types available:
           ┌─────────┬────────────────────────────┬─────────────┬────────────┐
           │         │                            │             │            │
           │ **Profile** │ **Redundancy** │ **Space** │  **Min/max** │
           │         ├────────┬────────┬──────────┤ **utilization** │  **devices** │
           │         │        │        │          │             │            │
           │         │ **Copies** │ **Parity** │ **Striping** │             │            │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ single  │   1    │        │          │        100% │   1/any    │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ DUP     │ 2 / 1  │        │          │         50% │ 1/any      │
           │         │ device │        │          │             │ ^(see note │
           │         │        │        │          │             │ 1)         │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ RAID0   │        │        │  1 to N  │        100% │ 1/any      │
           │         │        │        │          │             │ ^(see note │
           │         │        │        │          │             │ 5)         │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ RAID1   │   2    │        │          │         50% │   2/any    │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ RAID1C3 │   3    │        │          │         33% │   3/any    │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ RAID1C4 │   4    │        │          │         25% │   4/any    │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ RAID10  │   2    │        │  1 to N  │         50% │ 2/any      │
           │         │        │        │          │             │ ^(see note │
           │         │        │        │          │             │ 5)         │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ RAID5   │   1    │   1    │ 2 to N-1 │     (N-1)/N │ 2/any      │
           │         │        │        │          │             │ ^(see note │
           │         │        │        │          │             │ 2)         │
           ├─────────┼────────┼────────┼──────────┼─────────────┼────────────┤
           │         │        │        │          │             │            │
           │ RAID6   │   1    │   2    │ 3 to N-2 │     (N-2)/N │ 3/any      │
           │         │        │        │          │             │ ^(see note │
           │         │        │        │          │             │ 3)         │
           └─────────┴────────┴────────┴──────────┴─────────────┴────────────┘
    
               **Warning**
    
               It’s not recommended to create filesystems with RAID0/1/10/5/6
               profiles on partitions from the same device. Neither
               redundancy nor performance will be improved.
    
           _Note 1:_ DUP may exist on more than 1 device if it starts on a
           single device and another one is added. Since version 4.5.1,
           **mkfs.btrfs** will let you create DUP on multiple devices without
           restrictions.
    
           _Note 2:_ It’s not recommended to use 2 devices with RAID5. In that
           case, parity stripe will contain the same data as the data stripe,
           making RAID5 degraded to RAID1 with more overhead.
    
           _Note 3:_ It’s also not recommended to use 3 devices with RAID6,
           unless you want to get effectively 3 copies in a RAID1-like manner
           (but not exactly that).
    
           _Note 4:_ Since kernel 5.5 it’s possible to use RAID1C3 as
           replacement for RAID6, higher space cost but reliable.
    
           _Note 5:_ Since kernel 5.15 it’s possible to use (mount, convert
           profiles) RAID0 on one device and RAID10 on two devices.
    
       **PROFILE LAYOUT**
           For the following examples, assume devices numbered by 1, 2, 3 and
           4, data or metadata blocks A, B, C, D, with possible stripes eg.
           A1, A2 that would be logically A, etc. For parity profiles PA and
           QA are parity and syndrom, associated with the given stripe. The
           simple layouts single or DUP are left out. Actual physical block
           placement on devices depends on current state of the
           free/allocated space and may appear random. All devices are
           assumed to be present at the time of the blocks would have been
           written.
    
           RAID1
           ┌──────────┬──────────┬──────────┬──────────┐
           │ **device 1** │ **device 2** │ **device 3** │ **device 4** │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    A     │    D     │          │          │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    B     │          │          │    C     │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    C     │          │          │          │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    D     │    A     │    B     │          │
           └──────────┴──────────┴──────────┴──────────┘
    
           RAID1C3
           ┌──────────┬──────────┬──────────┬──────────┐
           │ **device 1** │ **device 2** │ **device 3** │ **device 4** │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    A     │    A     │    D     │          │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    B     │          │    B     │          │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    C     │          │    A     │    C     │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    D     │    D     │    C     │    B     │
           └──────────┴──────────┴──────────┴──────────┘
    
           RAID0
           ┌──────────┬──────────┬──────────┬──────────┐
           │ **device 1** │ **device 2** │ **device 3** │ **device 4** │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    A2    │    C3    │    A3    │    C2    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    B1    │    A1    │    D2    │    B3    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    C1    │    D3    │    B4    │    D1    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    D4    │    B2    │    C4    │    A4    │
           └──────────┴──────────┴──────────┴──────────┘
    
           RAID5
           ┌──────────┬──────────┬──────────┬──────────┐
           │ **device 1** │ **device 2** │ **device 3** │ **device 4** │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    A2    │    C3    │    A3    │    C2    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    B1    │    A1    │    D2    │    B3    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    C1    │    D3    │    PB    │    D1    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    PD    │    B2    │    PC    │    PA    │
           └──────────┴──────────┴──────────┴──────────┘
    
           RAID6
           ┌──────────┬──────────┬──────────┬──────────┐
           │ **device 1** │ **device 2** │ **device 3** │ **device 4** │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    A2    │    QC    │    QA    │    C2    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    B1    │    A1    │    D2    │    QB    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    C1    │    QD    │    PB    │    D1    │
           ├──────────┼──────────┼──────────┼──────────┤
           │          │          │          │          │
           │    PD    │    B2    │    PC    │    PA    │
           └──────────┴──────────┴──────────┴──────────┘
    


## DUP PROFILES ON A SINGLE DEVICE



           The mkfs utility will let the user create a filesystem with
           profiles that write the logical blocks to 2 physical locations.
           Whether there are really 2 physical copies highly depends on the
           underlying device type.
    
           For example, a SSD drive can remap the blocks internally to a
           single copy—thus deduplicating them. This negates the purpose of
           increased redundancy and just wastes filesystem space without
           providing the expected level of redundancy.
    
           The duplicated data/metadata may still be useful to statistically
           improve the chances on a device that might perform some internal
           optimizations. The actual details are not usually disclosed by
           vendors. For example we could expect that not all blocks get
           deduplicated. This will provide a non-zero probability of recovery
           compared to a zero chance if the single profile is used. The user
           should make the tradeoff decision. The deduplication in SSDs is
           thought to be widely available so the reason behind the mkfs
           default is to not give a false sense of redundancy.
    
           As another example, the widely used USB flash or SD cards use a
           translation layer between the logical and physical view of the
           device. The data lifetime may be affected by frequent plugging.
           The memory cells could get damaged, hopefully not destroying both
           copies of particular data in case of DUP.
    
           The wear levelling techniques can also lead to reduced redundancy,
           even if the device does not do any deduplication. The controllers
           may put data written in a short timespan into the same physical
           storage unit (cell, block etc). In case this unit dies, both
           copies are lost. BTRFS does not add any artificial delay between
           metadata writes.
    
           The traditional rotational hard drives usually fail at the sector
           level.
    
           In any case, a device that starts to misbehave and repairs from
           the DUP copy should be replaced! **DUP is not backup**.
    


## KNOWN ISSUES



           **SMALL FILESYSTEMS AND LARGE NODESIZE**
    
           The combination of small filesystem size and large nodesize is not
           recommended in general and can lead to various ENOSPC-related
           issues during mount time or runtime.
    
           Since mixed block group creation is optional, we allow small
           filesystem instances with differing values for _sectorsize_ and
           _nodesize_ to be created and could end up in the following
           situation:
    
               # mkfs.btrfs -f -n 65536 /dev/loop0
               btrfs-progs v3.19-rc2-405-g976307c
               See http://btrfs.wiki.kernel.org for more information.
    
               Performing full device TRIM (512.00MiB) ...
               Label:              (null)
               UUID:               49fab72e-0c8b-466b-a3ca-d1bfe56475f0
               Node size:          65536
               Sector size:        4096
               Filesystem size:    512.00MiB
               Block group profiles:
                 Data:             single            8.00MiB
                 Metadata:         DUP              40.00MiB
                 System:           DUP              12.00MiB
               SSD detected:       no
               Incompat features:  extref, skinny-metadata
               Number of devices:  1
               Devices:
                 ID        SIZE  PATH
                  1   512.00MiB  /dev/loop0
    
               # mount /dev/loop0 /mnt/
               mount: mount /dev/loop0 on /mnt failed: No space left on device
    
           The ENOSPC occurs during the creation of the UUID tree. This is
           caused by large metadata blocks and space reservation strategy
           that allocates more than can fit into the filesystem.
    


## AVAILABILITY



           **mkfs.btrfs** is part of btrfs-progs. Please refer to the btrfs wiki
           **http://btrfs.wiki.kernel.org******for further details.


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