Changes (feature/version)

Major features or significant feature enhancements by kernel version. For more information look below.

The version states at which version a feature has been merged into the mainline kernel. It does not tell anything about at which kernel version it is considered mature enough for production use. For an estimation on stability of features see [[Status]] page.


3.0 - scrub

Read all data and verify checksums, repair if possible.

3.2 - auto raid repair

Automatic repair of broken data from a good copy

3.2 - root backups

Save a few previous versions of the most imporant tree roots at commit time, used by -o recovery

3.3 - integrity checker

Optional infrastructure to verify integrity of written metadata blocks

3.3 - backref walking

Groundwork to allow tracking owner of blocks, used via inspect-internal

3.3 - restriper

RAID profiles can be changed on-line, balance filters

3.4 - big metadata blocks

Support for metadata blocks larger than page size


Default nodesize is 16k since btrfs-progs 3.12

3.4 - error handling

Generic infrastructure for graceful error handling (EIO)

3.5 - device statistics

Persistent statistics about device errors

3.5 - fsync speedup

Noticeable improvements in fsync() implementation

3.6 - qgroups

Subvolume-aware quotas

3.6 - send/receive

Ability to transfer one filesystem via a data stream (full or incremental) and apply the changes on a remote filesystem.

3.7 - extrefs

Hardlink count limit is lifted to 64k


Default since btrfs-progs 3.12

3.7 - hole puching

Implement the FALLOC_FL_PUNCH_HOLE mode of fallocate

3.8 - device replace

Efficient replacement of existing device (add/remove in one go)

3.9 - raid 5/6 (incomplete)

Basic support for RAD5/6 profiles, no crash resiliency, replace and scrub support

3.9 - snapshot-aware defrag

Defrag does not break links between shared extents (snapshots, reflinked files)


Disabled since 3.14 (and backported to some stable kernel versions) due to problems. Will be enabled in the future.

3.9 - lightweight send

A mode of send that does not add the actual file data to the stream

3.9 - on-line label set/get

Label editable on mounted filesystems

3.10 - skinny metadata

Reduced metadata size (format change) of extents


Default since btrfs-progs 3.18

3.10 - qgroup rescan

Sync qgroups with existing filesystem data

3.12 - uuid tree

A map of subvolume/UUID that vastly speeds up send/receive

3.12 - out-of-bound dedup

Support for deduplicating extents on a given set of files.

3.14 - no-holes

No extent representation for file holes (format change), may reduce overall metadata consumption

3.14 - feature bits in sysfs

/sys/fs/btrfs exports various bits about filesystem capabilities and feature support

3.16 - O_TMPFILE

Mode of open() to safely create a temporary file

3.16 - search ioctl v2

The extended SEARCH_TREE ioctl able to get more than a 4k data

3.18 - auto blockgroup reclaim

Automatically remove blockgroups (aka. chunks) that become completely empty.

3.19 - raid56: scrub, replace

Scrub and device replace works on RAID56 filesystems.


4.0 - store otime

Save creation time (otime) for all new files and directories. For future use, current tool cannot read it directly.

4.2 - rootid ioctl accessible

The INO_LOOKUP will return root id (id of the containing subvolume), unrestricted and to all users if the treeid is 0.

4.2 - dedupe possible on the same inode

The EXTENT_SAME ioctl will accept the same inode as source and destination (ranges must not overlap).

4.3 - trim all free space

Trim will be performed also on the space that’s not allocated by the chunks, not only free space within the allocated chunks.

4.4 - balance filter updates

Enhanced syntax and new balance filters: * limit=min..max * usage=min..max * stripes=min..max

4.5 - free space tree

Improved implementation of free space cache (aka v2), using b-trees.


Default since btrfs-progs 5.15, Kernel 4.9 fixes endianity bugs on big-endian machines, x86* is ok

4.5 - balance filter updates

Conversion to data/DUP profile possible through balance filters -- on single-device filesytem.


mkfs.btrfs allows creating DUP on single device in the non-mixed mode since 4.4

4.6 - max_inline default

The default value of max_inline changed to 2048.

4.6 - read features from control device

The existing ioctl GET_SUPPORTED_FEATURES can be now used on the control device (/dev/btrfs-control) and returns the supported features without any mounted filesystem.

4.7 - delete device by id

Add new ioctl RM_DEV_V2, pass device to be deleted by its ID.

4.7 - more renameat2 modes

Add support for RENAME_EXCHANGE and RENAME_WHITEOUT to renameat2 syscall. This also means that overlayfs is now supported on top of btrfs.

4.7 - balance filter updates

Conversion to data/DUP profile possible through balance filters -- on multiple-device filesystems.


mkfs.btrfs allows creating DUP on multiple devices since 4.5.1

4.12 - raid56: auto repair

Scrub will attempt auto-repair (similar to raid1/raid10)

4.13 - statx

Support for the enhanced statx syscall; file creation timestamp

4.13 - sysfs qgroups override

qgroups: new sysfs control file to allow temporary quota override with CAP_SYS_RESOURCE

4.13 - deprecated mount option alloc_start

That was a debugging helper, not used and not supposed to be used nowadays.

4.14 - ZSTD compression

New compression algorithm ZSTD, supposedly better ratio/speed performance.

4.14 - improved degraded mount

Allow degraded mount based on the chunk constraints, not device number constraints. Eg. when one device is missing but the remaining one holds all single chunks.

4.14 - deprecated user transaction ioctl

BTRFS_IOC_TRANS_START and BTRFS_IOC_TRANS_END, no known users, tricky to use; scheduled to be removed in 4.17

4.14 - refine SSD optimizations

The mount option ssd does not make any assumptions about block layout or management by the device anymore, leaving only the speedups based on low seek cost active. This could avoid some corner cases leading to excessive fragmentation. The story so far.

4.15 - overlayfs

Overlayfs can now use btrfs as the lower filesystem.

4.15 - ref-verify

Debugging functionality to verify extent references. New mount option <i>ref-verify</i>, must be built with CONFIG_BTRFS_FS_REF_VERIFY.

4.15 - zlib level

Allow to set the zlib compression level via mount option, eg. like compress=zlib:9. The levels match the default zlib compression levels. The default is 3.

4.15 - v2 of LOGICAL_INO ioctl

An enhanced version of ioctl that can translate logical extent offset to inode numbers, “who owns this block”. For certain usecases the V1 performs bad and this is addressed by V2. [ Read more.]

4.15 - compression heuristics

Apply a few heuristics to the data before they’re compressed to decide if it’s likely to gain any space savings. The methods: frequency sampling, repeated pattern detection, Shannon entropy calculation.

4.16 - fallocate: zero range

Mode of the [ fallocate] syscall to zero file range.

4.17 - removed user transaction ioctl

deprecated in 4.14, see above

4.17 - rmdir on subvolumes

Allow rmdir to delete an empty subvolume.

4.18 - XFLAGS ioctl

Add support for ioctl FS_IOC_FSSETXATTR/FS_IOC_FSGETXATTR, successor of FS_IOC_SETFLAGS/FS_IOC_GETFLAGS ioctl. Currently supports: APPEND, IMMUTABLE, NOATIME, NODUMP, SYNC. Note that the naming is very confusing, though it’s named xattr, it does not mean the extended attributes. It should be referenced as extended inode flags or xflags.

4.18 - EXTENT_SAME ioctl / 16MiB chunks

The range for out-of-band deduplication implemented by the EXTENT_SAME ioctl will split the range into 16MiB chunks. Up to now this was the overall limit and effectively only the first 16MiB was deduplicated.

4.18 - GET_SUBVOL_INFO ioctl

New ioctl to read subvolume information (id, directory name, generation, flags, UUIDs, time). This does not require root permissions, only the regular access to to the subvolume.


New ioctl to enumerate subvolume references of a given subvolume. This does not require root permissions, only the regular access to to the subvolume.

4.18 - INO_LOOKUP_USER ioctl

New ioctl to lookup path by inode number. This does not require root permissions, only the regular access to to the subvolume, unlike the INO_LOOKUP ioctl.

4.19 - defrag ro/rw

Allow to run defrag on files that are normally accesible for read-write, but are currently opened in read-only mode.


5.0 - swapfile

With some limitations where COW design does not work well with the swap implementation (nodatacow file, no compression, cannot be snapshotted, not possible on multiple devices, …), as this is the most restricted but working setup, we’ll try to improve that in the future

5.0 - metadata uuid

An optional incompat feature to assign a new filesystem UUID without overwriting all metadata blocks, stored only in superblock, unlike what btrfstune -u

5.1 - FORGET_DEV ioctl

Unregister devices previously added by the scan ioctl, same effect as if the kernel module is reloaded.

5.1 - zstd level

Allow to set the zstd compression level via mount option, eg. like compress=zstd:9. The levels match the default zstd compression levels. The default is 3, maximum is 15.

5.2 - pre-write checks

Verify metadata blocks before submitting them to the devices. This can catch consistency problems or bitflips.

5.5 - more checksums

New checksum algorithms: xxhash (64b), SHA256 (256b), BLAKE2b (256b).

5.5 - RAID1C34

RAID1 with 3- and 4- copies (over all devices).

5.6 - async discard

Mode of discard (mount -o discard=async) that merges freed extents to larger chunks and submits them for discard in a less intrusive way

5.6 - device info in sysfs

More information about device state can be found in per-filesystem sysfs directory.

5.7 - reflink/clone works on inline files

Inline files can be reflinked to the tail extent of other files

5.7 - faster balance cancel

More cancellation points in balance that will shorten the time to stop processing once <tt>btrfs balance cancel</tt> is called.

5.7 - removed flag BTRFS_SUBVOL_CREATE_ASYNC

Remove support of flag BTRFS_SUBVOL_CREATE_ASYNC from subvolume creation ioctl.

5.7 - v2 of snapshot deletion ioctl

New ioctl BTRFS_IOC_SNAP_DESTROY_V2, deletion by subvolume id is now possible.

5.9 - mount option rescue

Unified mount option for actions that may help to access a damaged filesystem. Now supports: nologreplay, usebackuproot

5.9 - qgroups in sysfs

The information about qgroup status and relations is exported in /sys/fs/UUID/qgroups

5.9 - FS_INFO ioctl

Export more information: checksum type, checksum size, generation, metadata_uuid

5.10 - exclusive ops in sysfs

Export which filesystem exclusive operation is running (balance, resize, device add/delete/relpace, …)

5.11 - remove inode_cache

Remove inode number caching feature (mount -o inode_cache)

5.11 - more rescue=

Additional modes for mount option rescue=: ignorebadroots/ibadroots, ignoredatacsums/idatacsums. All are exported in sysfs.

5.12 - zoned mode

Support for zoned devices with special allocation/write mode to fixed-size zones. See [[Zoned]].

5.13 - supported_sectorsizes in sysfs

List supported sector sizes in sysfs file /sys/fs/btrfs/features/supported_sectorsizes

5.14 - sysfs scrub bw limit

Tunable bandwidth limit (/sys/fs/btrfs/FSID/devinfo/DEVID/scrub_speed_max) for scrub (and device replace) for a given device.

5.14 - sysfs device stats

The device stats can be also found in /sys/fs/btrfs/FSID/devinfo/DEVID/error_stats.

5.14 - cancellable resize, device delete

The filesystem resize and device delete operations can be cancelled by specifying cancel as the device name.

5.14 - property value reset

Change how empty value is interpreted. New behaviour will delete the value and reset it to default. This affects btrfs.compression where value no sets NOCOMPRESS bit while empty value resets all compression settings (either compression or NOCOMPRESS bit).

5.15 - fsverity

The fs-verity is a support layer that filesystems can hook into to support transparent integrity and authenticity protection of read-only files.

5.15 - idmapped mount

Support mount with uid/gid mapped according to another namespace.

5.16 - ZNS in zoned

Zoned namespaces. ,

5.17 - send and relocation

Send and relocation (balance, device remove, shrink, block group reclaim) can now work in parallel

5.17 - device add vs balance

It is possible to add a device with paused balance


Since kernel 5.17.7 and btrfs-progs 5.17.1

5.17 - no warning with flushoncommit

Mounting with -o flushoncommit does not triggher the (harmless) warning at each transaction commit


Also backported to 5.15.27 and 5.16.13

5.18 - zoned and DUP metadata

DUP metadata works with zoned mode

5.18 - encoded data ioctl

New ioctls to read and write pre-encoded data (ie. no transformation and directly written as extents), now works for compressed data

5.18 - removed balance ioctl v1

The support for ioctl BTRFS_IOC_BALANCE has been removed, superseded by BTRFS_IOC_BALANCE_V2m long time ago