zfs on gmirror slice

Dimitry Andric dimitry at andric.com
Wed Sep 2 14:10:10 UTC 2009

On 2009-09-02 10:27, Mark Stapper wrote:
> self-healing sounds very nice, but with mirrorring you have data on two
> discs, so in that case there no "healing" involved, it's just
> checksumming and reading the non-corrupted copy.
> From the gmirror manpage: "All operations like failure detection, stale
> component detection, rebuild of stale components, etc. are also done
> automatically."
> This would indicate the same functionality, with a much less fancy name.

Not really. ZFS can checksum the actual file data, while gmirror can
only detect errors it gets told about by the underlying disk.  E.g. if
the disk silently corrupts data, you will never know about it.

Also, if gmirror needs to resynchronize, it must resynchronize the whole
disk, since it can't detect which specific parts of it were corrupted.
ZFS synchronizes on demand.

There are also some other advantages to ZFS mirroring, see pages 15 and
further of these slides:


More information about the freebsd-stable mailing list