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Message-ID: <CAB9VWqDCM5mwnd0nQV8OEcbEa7mt=ySkqWdhbsGk=VpdmY2pog@mail.gmail.com>
Date: Fri, 25 May 2012 18:38:54 +0200
From: Alexander Block <ablock84@...glemail.com>
To: Andreas Dilger <adilger@...ger.ca>
Cc: Josef Bacik <josef@...hat.com>,
"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: atime and filesystems with snapshots (especially Btrfs)
On Fri, May 25, 2012 at 6:28 PM, Andreas Dilger <adilger@...ger.ca> wrote:
> On 2012-05-25, at 9:59, Alexander Block <ablock84@...glemail.com> wrote:
>
> Are you talking about the atime for the primary copy, or the atime for the snapshots? IMHO, the atime should not be updated for a snapshot unless it is explicitly mounted r/w, or it isn't really a good snapshot.
>
Snapshots are by default r/w but can be created r/o explicitly. But
that doesn't matter for the normal use case where you snapshot / and
continue working on /. After snapshotting, all metadata is shared
between the two subvolumes, but when a metadata block in one of both
subvolume changes (no matter which one), this one metadata block get's
cowed and unshared and uses up more space.
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