Re: selectively disabling atime updates?

["J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>]

On Jun 11, 2012, at 8:25 PM, Manuel Bouyer wrote:

> 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.

Or better with `fsck_ffs -x /snapshot/backup' to use a file system
external snapshot.

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

--
Juergen Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig 
(Germany)