On 1 April 2011 19:38, Adam Vande More <amvandem...@gmail.com> wrote: > On Fri, Apr 1, 2011 at 12:02 PM, Chris H <chris#@1command.com> wrote: > >> On Fri, April 1, 2011 6:29 am, Marko Lerota wrote: >> > I read that ZFS don't need fsck because the files are always consistent >> on >> filesystem regardless >> > of power loses. That the corruption can occur only if disks are damaged. >> But not >> > when power goes down. >> >> Complete nonsense. The information you read was false. >> > > No, it's really not. ZFS's lack of recovery tools at least in the > beginning were basically non existent. This is because ZFS uses a COW > model with an atomic data management unit design which by it's nature > addresses thing like fsck, and sudden power loss.
Indeed. By copy on write and its' b-tree ZFS ensures consistency, however, this does not mean that there's no data loss. Writes are done in a transaction group, including an updated version of the b-tree. Only if all the new information has been written successfully the new b-tree "is tagged as valid" and becomes active. (Which is the reason why you can't rm files in a full pool.) If there's a power failure during a write ZFS recovers automatically during the mount (or zpool import, not sure on this one) _by deleting the inconsistent data_ and thus reverting to the last known state. Additionally, a transaction group may consist of several writes that reach a total size (I think 128Kb per default). If there are small and slow writes (e.g.to a Logfie) these are cached up to 30 seconds. If a power failure or any other kind of discruptive failure happens you'll loose all the information cached. _______________________________________________ freebsd-stable@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-stable To unsubscribe, send any mail to "freebsd-stable-unsubscr...@freebsd.org"
