Re: selectively disabling atime updates?

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Jun 11, 2012 at 01:18:17PM -0400, Greg Troxel wrote:
> 
> Thor Lancelot Simon <tls%panix.com@localhost> writes:
> 
> > On Mon, Jun 11, 2012 at 05:52:27PM +0200, Edgar Fu? wrote:
> >> > Yes, but I have to question whether and why it would improve performance
> >> > in this case.  The stream of atime updates is still happening on the
> >> > underlying filesystem, and that is still where you will be doing almost
> >> > all of your reads from.
> >>
> >> My intent was to mount the snapshot ro,noatime and operate on that.
> >> Am I again missing something stupid?
> 
> You should only need ro; it doesn't make sense to talk about atime
> updates or not when you aren't writing to the underlying block device.
> 
> > Hm.  No, I don't think so.  I wonder -- will the snapshot management code
> > cause the resulting snapshot to be in a consistent state so access through
> > the filesystem is safe?
> 
> I would say that it should or it's a bug; it seems the whole point of
> snapshots is to get a consistent view of a filesystem.
> Given that the normal use case seems to be things like
> snapshot/dump/drop-snapshot, I would think that if it were buggy there's
> a decent chance there would have been complaints by now.

You can test with fsck_ffs -X; I use it from daily scripts on some systems,
and it does the job.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--