OpenZFS on Linux 0.6.4

=== NEW FEATURE FLAGS ===

The following new features can be enabled by running 'zpool upgrade'
after first installing the new release and then rebooting your system.
A reboot is required to load the new kernel modules. By default, no
new features will be automatically enabled.

WARNING: Once the new pool features are enabled you will be unable
to rollback to an older version of ZFS which does not support this
functionality.

GRUB: Users who rely on ZFS for their root file system are strongly
cautioned against enabling these features on their root pool. The
version of GRUB provided by most distributions does not yet support
this functionality. Consequently GRUB will be unable to access the
contents of /boot which will prevent your system from booting. You
may only safely enable the new features on your root pool if /boot
is located on a non-ZFS filesystem or if a patched version of GRUB
is available for your distribution. Currently patched GRUB packages
are only provided though the ZFS on Linux repositories for Debian.

* spacemap_histogram

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.

* extensible_dataset

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.

* bookmarks

This feature enables use of the zfs bookmark subcommand. Bookmarks
mark the point in time when a snapshot was created, they can be used
as the incremental source for a zfs send command. All bookmarks in
the pool can be listed by running zfs list -t bookmark -r poolname.

* enabled_txg

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.

* hole_birth

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.

* embedded_data

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.

Full changelog:

https://github.com/zfsonlinux/zfs/releases