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) – illumos

zpool-features(7) – FreeBSD

Feature flags implementation

Feature Flag	Read-Only Compatible	DragonFlyBSD	FreeBSD			Joyent	NetBSD	OmniOSCE			OpenZFS	OpenZFS on OSX			ZFS on Linux
		zfsport	11.2.0	12.0.0	head	master	main	r151026	r151028	master	master	1.8.0	1.8.1	master	0.6.5.11	0.7.12	master
encryption	no	no	no	no	no	no	no	no	no	no	no	yes	yes	yes	no	no	yes
resilver_defer	yes	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	yes
async_destroy	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
bookmarks	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
device_removal	no	no	yes	yes	yes	yes	no	yes	yes	yes	yes	yes	yes	yes	no	no	yes
embedded_data	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
empty_bpobj	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
enabled_txg	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
extensible_dataset	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
hole_birth	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
obsolete_counts	yes	no	yes	yes	yes	yes	no	yes	yes	yes	yes	yes	yes	yes	no	no	yes
spacemap_histogram	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
spacemap_v2	yes	no	no	yes	yes	yes	no	yes	yes	yes	yes	yes	yes	yes	no	no	yes
zpool_checkpoint	yes	no	yes	yes	yes	yes	no	yes	yes	yes	yes	yes	yes	yes	no	no	yes
filesystem_limits	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
multi_vdev_crash_dump	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	no	yes	yes
edonr	no	no	no	no	no	yes	no	yes	yes	yes	yes	yes	yes	yes	no	yes	yes
lz4_compress	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
sha512	no	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	no	yes	yes
skein	no	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	no	yes	yes
large_block	no	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes	yes
allocation_classes	yes	no	no	no	no	no	no	no	no	no	no	no	no	yes	no	no	yes
large_dnode	no	no	no	no	no	no	no	no	no	no	no	no	no	yes	no	yes	yes
project_quota	yes	no	no	no	no	no	no	no	no	no	no	no	no	no	no	no	yes
userobj_accounting	yes	no	no	no	no	no	no	no	no	no	no	no	no	no	no	yes	yes

Table legend

• no = not implemented
• yes = implemented

Source: [1] as of 20190121