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 | no | no | no | yes |
large_dnode | no | no | no | no | no | no | no | no | no | no | no | no | no | no | 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