[ale] Fwd: periodic fsck was Re: [patch] ext2/3: document conditions when reliable operation is possible

[Ed Cashin]

On Tue, Nov 10, 2009 at 7:55 AM, Rev. Johnny Healey <rev.null at gmail.com> wrote:
> I believe the reason that you can't fsck a mounted fs is because of the
> chance of writes during the fsck.  But when you make a snapshot, it doesn't
> get mounted until you explicitely mount it somewhere.

Yes, it should be just like running fsck on an unmounted filesystem after
a power failure (no clean shutdown), if I understand correctly.

In that situation, you can get some errors reported for an otherwise healthy
filesystem, just because it wasn't left in a 100% consistent state.
If the power
hadn't gone out, those inconsistencies would have been corrected in the
following seconds.  With a snapshot, though, those same inconsistencies
will appear, even though there's no persistent problem with the filesystem.

So I would think that unless the fs was unmounted before the snapshot
was taken, the
admin wouldn't be able to tell between errors related to the fact that the
snapshot was taken on a live filesystem and errors related to serious and
persistent problems.

-- 
  Ed Cashin <ecashin at noserose.net>
  http://noserose.net/e/
  http://www.coraid.com/