This feature enables support for separate allocation classes.

This feature becomes active when a dedicated allocation class vdev (dedup or special) is created with the zpool create or zpool add subcommands. With device removal, it can be returned to the enabled state if all the dedicated allocation class vdevs are removed.

Destroying a file system requires traversing all of its data in order to return its used space to the pool. Without async_destroy the file system is not fully removed until all space has been reclaimed. If the destroy operation is interrupted by a reboot or power outage the next attempt to open the pool will need to complete the destroy operation synchronously.

When async_destroy is enabled the file system's data will be reclaimed by a background process, allowing the destroy operation to complete without traversing the entire file system. The background process is able to resume interrupted destroys after the pool has been opened, eliminating the need to finish interrupted destroys as part of the open operation. The amount of space remaining to be reclaimed by the background process is available through the freeing property.

This feature is only active while freeing is non-zero.

This feature enables use of the zfs bookmark subcommand.

This feature is active while any bookmarks exist in the pool. All bookmarks in the pool can be listed by running zfs list -t bookmark -r poolname.

This feature enables the creation and management of larger bookmarks which are needed for other features in ZFS.

This feature becomes active when a v2 bookmark is created and will be returned to the enabled state when all v2 bookmarks are destroyed.

This feature enables additional bookmark accounting fields, enabling the written#<bookmark> property (space written since a bookmark) and estimates of send stream sizes for incrementals from bookmarks.

This feature becomes active when a bookmark is created and will be returned to the enabled state when all bookmarks with these fields are destroyed.

This feature enables the ability for the zpool attach and zpool replace subcommands to perform sequential reconstruction (instead of healing reconstruction) when resilvering.

Sequential reconstruction resilvers a device in LBA order without immediately verifying the checksums. Once complete a scrub is started which then verifies the checksums. This approach allows full redundancy to be restored to the pool in the minimum amount of time. This two phase approach will take longer than a healing resilver when the time to verify the checksums is included. However, unless there is additional pool damage no checksum errors should be reported by the scrub. This feature is incompatible with raidz configurations.

This feature becomes active while a sequential resilver is in progress, and returns to enabled when the resilver completes.

This feature enables the zpool remove subcommand to remove top-level vdevs, evacuating them to reduce the total size of the pool.

This feature becomes active when the zpool remove subcommand is used on a top-level vdev, and will never return to being enabled.

This feature enables the use of the Edon-R hash algorithm for checksum, including for nopwrite (if compression is also enabled, an overwrite of a block whose checksum matches the data being written will be ignored). In an abundance of caution, Edon-R requires verification when used with dedup: zfs set dedup=edonr,verify. See zfs(8).

Edon-R is a very high-performance hash algorithm that was part of the NIST SHA-3 competition. It provides extremely high hash performance (over 350% faster than SHA-256), but was not selected because of its unsuitability as a general purpose secure hash algorithm. This implementation utilizes the new salted checksumming functionality in ZFS, which means that the checksum is pre-seeded with a secret 256-bit random key (stored on the pool) before being fed the data block to be checksummed. Thus the produced checksums are unique to a given pool.

When the edonr feature is set to enabled, the administrator can turn on the edonr checksum on any dataset using the zfs set checksum=edonr. See zfs(8). This feature becomes active once a checksum property has been set to edonr, and will return to being enabled once all filesystems that have ever had their checksum set to edonr are destroyed.

FreeBSD does not support the edonr feature.

This feature improves the performance and compression ratio of highly-compressible blocks. Blocks whose contents can compress to 112 bytes or smaller can take advantage of this feature.

When this feature is enabled, the contents of highly-compressible blocks are stored in the block "pointer" itself (a misnomer in this case, as it contains the compressed data, rather than a pointer to its location on disk). Thus the space of the block (one sector, typically 512 bytes or 4KB) is saved, and no additional i/o is needed to read and write the data block.

This feature becomes active as soon as it is enabled and will never return to being enabled.

This feature increases the performance of creating and using a large number of snapshots of a single filesystem or volume, and also reduces the disk space required.

When there are many snapshots, each snapshot uses many Block Pointer Objects (bpobj's) to track blocks associated with that snapshot. However, in common use cases, most of these bpobj's are empty. This feature allows us to create each bpobj on-demand, thus eliminating the empty bpobjs.

This feature is active while there are any filesystems, volumes, or snapshots which were created after enabling this feature.

Once this feature is enabled ZFS records the transaction group number in which new features are enabled. This has no user-visible impact, but other features may depend on this feature.

This feature becomes active as soon as it is enabled and will never return to being enabled.

This feature enables the creation and management of natively encrypted datasets.

This feature becomes active when an encrypted dataset is created and will be returned to the enabled state when all datasets that use this feature are destroyed.

This feature allows more flexible use of internal ZFS data structures, and exists for other features to depend on.

This feature will be active when the first dependent feature uses it, and will be returned to the enabled state when all datasets that use this feature are destroyed.

This feature enables filesystem and snapshot limits. These limits can be used to control how many filesystems and/or snapshots can be created at the point in the tree on which the limits are set.

This feature is active once either of the limit properties has been set on a dataset. Once activated the feature is never deactivated.

This feature has/had bugs, the result of which is that, if you do a zfs send -i (or -R, since it uses -i) from an affected dataset, the receiver will not see any checksum or other errors, but the resulting destination snapshot will not match the source. Its use by zfs send -i has been disabled by default. See the send_holes_without_birth_time module parameter in zfs-module-parameters(5).

This feature improves performance of incremental sends (zfs send -i) and receives for objects with many holes. The most common case of hole-filled objects is zvols.

An incremental send stream from snapshot A to snapshot B contains information about every block that changed between A and B. Blocks which did not change between those snapshots can be identified and omitted from the stream using a piece of metadata called the 'block birth time', but birth times are not recorded for holes (blocks filled only with zeroes). Since holes created after A cannot be distinguished from holes created before A, information about every hole in the entire filesystem or zvol is included in the send stream.

For workloads where holes are rare this is not a problem. However, when incrementally replicating filesystems or zvols with many holes (for example a zvol formatted with another filesystem) a lot of time will be spent sending and receiving unnecessary information about holes that already exist on the receiving side.

Once the hole_birth feature has been enabled the block birth times of all new holes will be recorded. Incremental sends between snapshots created after this feature is enabled will use this new metadata to avoid sending information about holes that already exist on the receiving side.

This feature becomes active as soon as it is enabled and will never return to being enabled.

The large_block feature allows the record size on a dataset to be set larger than 128KB.

This feature becomes active once a dataset contains a file with a block size larger than 128KB, and will return to being enabled once all filesystems that have ever had their recordsize larger than 128KB are destroyed.

The large_dnode feature allows the size of dnodes in a dataset to be set larger than 512B.

This feature becomes active once a dataset contains an object with a dnode larger than 512B, which occurs as a result of setting the dnodesize dataset property to a value other than legacy. The feature will return to being enabled once all filesystems that have ever contained a dnode larger than 512B are destroyed. Large dnodes allow more data to be stored in the bonus buffer, thus potentially improving performance by avoiding the use of spill blocks.

This feature improves performance for heavily-fragmented pools, especially when workloads are heavy in random-writes. It does so by logging all the metaslab changes on a single spacemap every TXG instead of scattering multiple writes to all the metaslab spacemaps.

This feature becomes active as soon as it is enabled and will never return to being enabled.

lz4 is a high-performance real-time compression algorithm that features significantly faster compression and decompression as well as a higher compression ratio than the older lzjb compression. Typically, lz4 compression is approximately 50% faster on compressible data and 200% faster on incompressible data than lzjb. It is also approximately 80% faster on decompression, while giving approximately 10% better compression ratio.

When the lz4_compress feature is set to enabled, the administrator can turn on lz4 compression on any dataset on the pool using the zfs(8) command. Please note that doing so will immediately activate the lz4_compress feature on the underlying pool using the zfs(8) command. Also, all newly written metadata will be compressed with lz4 algorithm. Since this feature is not read-only compatible, this operation will render the pool unimportable on systems without support for the lz4_compress feature.

This feature becomes active as soon as it is enabled and will never return to being enabled.

This feature allows a dump device to be configured with a pool comprised of multiple vdevs. Those vdevs may be arranged in any mirrored or raidz configuration.

When the multi_vdev_crash_dump feature is set to enabled, the administrator can use the dumpadm(1M) command to configure a dump device on a pool comprised of multiple vdevs.

Under FreeBSD and Linux this feature is registered for compatibility but not used. New pools created under FreeBSD and Linux will have the feature enabled but will never transition to active. This functionality is not required in order to support crash dumps under FreeBSD and Linux. Existing pools where this feature is active can be imported.

This feature is an enhancement of device_removal, which will over time reduce the memory used to track removed devices. When indirect blocks are freed or remapped, we note that their part of the indirect mapping is "obsolete", i.e. no longer needed.

This feature becomes active when the zpool remove subcommand is used on a top-level vdev, and will never return to being enabled.

This feature allows administrators to account the spaces and objects usage information against the project identifier (ID).

The project ID is new object-based attribute. When upgrading an existing filesystem, object without project ID attribute will be assigned a zero project ID. After this feature is enabled, newly created object will inherit its parent directory's project ID if the parent inherit flag is set (via chattr +/-P or zfs project [-s|-C]). Otherwise, the new object's project ID will be set as zero. An object's project ID can be changed at anytime by the owner (or privileged user) via chattr -p $prjid or zfs project -p $prjid.

This feature will become active as soon as it is enabled and will never return to being disabled. Each filesystem will be upgraded automatically when remounted or when new file is created under that filesystem. The upgrade can also be triggered on filesystems via `zfs set version=current <pool/fs>`. The upgrade process runs in the background and may take a while to complete for the filesystems containing a large number of files.

This feature enables the use of the redacted zfs send. Redacted zfs send creates redaction bookmarks, which store the list of blocks redacted by the send that created them. For more information about redacted send, see zfs(8).

This feature enables the receiving of redacted zfs send streams. Redacted zfs send streams create redacted datasets when received. These datasets are missing some of their blocks, and so cannot be safely mounted, and their contents cannot be safely read. For more information about redacted receive, see zfs(8).

This feature allows zfs to postpone new resilvers if an existing one is already in progress. Without this feature, any new resilvers will cause the currently running one to be immediately restarted from the beginning.

This feature becomes active once a resilver has been deferred, and returns to being enabled when the deferred resilver begins.

This feature enables the use of the SHA-512/256 truncated hash algorithm (FIPS 180-4) for checksum and dedup. The native 64-bit arithmetic of SHA-512 provides an approximate 50% performance boost over SHA-256 on 64-bit hardware and is thus a good minimum-change replacement candidate for systems where hash performance is important, but these systems cannot for whatever reason utilize the faster skein and edonr algorithms.

When the sha512 feature is set to enabled, the administrator can turn on the sha512 checksum on any dataset using zfs set checksum=sha512. See zfs(8). This feature becomes active once a checksum property has been set to sha512, and will return to being enabled once all filesystems that have ever had their checksum set to sha512 are destroyed.

This feature enables the use of the Skein hash algorithm for checksum and dedup. Skein is a high-performance secure hash algorithm that was a finalist in the NIST SHA-3 competition. It provides a very high security margin and high performance on 64-bit hardware (80% faster than SHA-256). This implementation also utilizes the new salted checksumming functionality in ZFS, which means that the checksum is pre-seeded with a secret 256-bit random key (stored on the pool) before being fed the data block to be checksummed. Thus the produced checksums are unique to a given pool, preventing hash collision attacks on systems with dedup.

When the skein feature is set to enabled, the administrator can turn on the skein checksum on any dataset using zfs set checksum=skein. See zfs(8). This feature becomes active once a checksum property has been set to skein, and will return to being enabled once all filesystems that have ever had their checksum set to skein are destroyed.

This features allows ZFS to maintain more information about how free space is organized within the pool. If this feature is enabled, ZFS will set this feature to active when a new space map object is created or an existing space map is upgraded to the new format. Once the feature is active, it will remain in that state until the pool is destroyed.

This feature enables the use of the new space map encoding which consists of two words (instead of one) whenever it is advantageous. The new encoding allows space maps to represent large regions of space more efficiently on-disk while also increasing their maximum addressable offset.

This feature becomes active once it is enabled, and never returns back to being enabled.

This feature allows administrators to account the object usage information by user and group.

This feature becomes active as soon as it is enabled and will never return to being enabled. Each filesystem will be upgraded automatically when remounted, or when new files are created under that filesystem. The upgrade can also be started manually on filesystems by running `zfs set version=current <pool/fs>`. The upgrade process runs in the background and may take a while to complete for filesystems containing a large number of files.

This feature enables the zpool checkpoint subcommand that can checkpoint the state of the pool at the time it was issued and later rewind back to it or discard it.

This feature becomes active when the zpool checkpoint subcommand is used to checkpoint the pool. The feature will only return back to being enabled when the pool is rewound or the checkpoint has been discarded.

zstd is a high-performance compression algorithm that features a combination of high compression ratios and high speed. Compared to gzip, zstd offers slighty better compression at much higher speeds. Compared to lz4, zstd offers much better compression while being only modestly slower. Typically, zstd compression speed ranges from 250 to 500 MB/s per thread and decompression speed is over 1 GB/s per thread.

When the zstd feature is set to enabled, the administrator can turn on zstd compression of any dataset by running `zfs set compress=zstd <pool/fs>`.

This feature becomes active once a compress property has been set to zstd, and will return to being enabled once all filesystems that have ever had their compress property set to zstd are destroyed.