Feature Flags

ZFS on-disk formats were originally versioned with a single number, which increased whenever the format changed. The numbered approach was suitable when development of ZFS was driven by a single organisation.

For distributed development of OpenZFS, version numbering was unsuitable. Any change to the number would have required agreement, across all implementations, of each change to the on-disk format.

OpenZFS feature flags – an alternative to traditional version numbering – allow a uniquely named pool property for each change to the on-disk format. This approach supports:

  • format changes that are independent

  • format changes that depend on each other.

Compatibility

Where all features that are used by a pool are supported by multiple implementations of OpenZFS, the on-disk format is portable across those implementations.

Features that are exclusive when enabled should be periodically ported to all distributions.

Reference materials

ZFS Feature Flags (Christopher Siden, 2012-01, in the Internet Archive Wayback Machine) in particular: “… Legacy version numbers still exist for pool versions 1-28 …”.

zpool-features(5) man page - OpenZFS

zpool-features (5) – illumos

Feature flags implementation per OS

ZFS Feature Matrix
Feature FlagRead-Only
Compatible
OpenZFS (Linux, FreeBSD 13+)FreeBSD pre OpenZFSIllumosJoyentNetBSDNexentaOmniOS CEOpenZFS on OS X
0.6.5.110.7.130.8.62.0.411.4.012.1.012.2.0mastermaster9.2main4.0.5-FP5.3masterr151036r151038master1.9.21.9.31.9.4master
org.zfsonlinux:allocation_classesyesnonoyesyesnonoyesyesyesnononononoyesyesyesyesyesyesyes
com.delphix:async_destroyyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.datto:bookmark_v2nononoyesyesnononoyesyesnononononoyesyesyesyesyesyesyes
com.delphix:bookmark_writtennonononoyesnonononononononononononononononono
com.delphix:bookmarksyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.nexenta:class_of_storageyesnononononononononononoyesyesyesnonononononono
org.openzfs:device_rebuildyesnononoyesnonononononononononononononononono
com.delphix:device_removalnononoyesyesyesyesyesyesyesnononoyesyesyesyesyesyesyesyesyes
org.illumos:edonrnonoyesyesyesnononoyesyesnononoyesyesyesyesyesyesyesyesyes
com.delphix:embedded_datanoyesyesyesyesyesyesyesyesyesyesyesnoyesyesyesyesyesyesyesyesyes
com.delphix:empty_bpobjyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.delphix:enabled_txgyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.datto:encryptionnononoyesyesnononoyesyesnononononoyesyesyesyesyesyesyes
com.delphix:extensible_datasetnoyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.joyent:filesystem_limitsyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.delphix:hole_birthnoyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
org.open-zfs:large_blocksnoyesyesyesyesyesyesyesyesyesyesyesnoyesyesyesyesyesyesyesyesyes
org.zfsonlinux:large_dnodenonoyesyesyesnonoyesyesyesnononononoyesyesyesyesyesyesyes
com.delphix:livelistyesnononoyesnonononononononononononononononono
com.delphix:log_spacemapyesnononoyesnononoyesyesnononononoyesyesyesnononono
org.illumos:lz4_compressnoyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.nexenta:meta_devicesyesnononononononononononoyesyesyesnonononononono
com.joyent:multi_vdev_crash_dumpnonoyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.delphix:obsolete_countsyesnonoyesyesyesyesyesyesyesnononoyesyesyesyesyesyesyesyesyes
org.zfsonlinux:project_quotayesnonoyesyesnononoyesyesnononononoyesyesyesyesyesyesyes
com.delphix:redacted_datasetsnonononoyesnonononononononononononononononono
com.delphix:redaction_bookmarksnonononoyesnonononononononononononononononono
com.datto:resilver_deferyesnonoyesyesnononoyesyesnononononoyesyesyesyesyesyesyes
org.illumos:sha512nonoyesyesyesyesyesyesyesyesyesyesnoyesyesyesyesyesyesyesyesyes
org.illumos:skeinnonoyesyesyesyesyesyesyesyesyesyesnoyesyesyesyesyesyesyesyesyes
com.delphix:spacemap_histogramyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyesyes
com.delphix:spacemap_v2yesnonoyesyesyesyesyesyesyesnononononoyesyesyesyesyesyesyes
org.zfsonlinux:userobj_accountingyesnoyesyesyesnononoyesyesnononononoyesyesyesyesyesyesyes
com.nexenta:vdev_propertiesyesnononononononononononoyesyesyesnonononononono
com.nexenta:wbcnononononononononononononoyesyesnonononononono
com.delphix:zpool_checkpointyesnonoyesyesyesyesyesyesyesnononononoyesyesyesyesyesyesyes
org.freebsd:zstd_compressnonononoyesnonononononononononononononononono

Table generates by parsing manpages for feature flags, and is entirely dependent on good, accurate documentation.
Last updated on 2021-06-17T20:43:37.640518Z using compatibility_matrix.py.