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Date:      Tue, 04 Sep 2018 03:26:13 +0000
From:      bugzilla-noreply@freebsd.org
To:        standards@FreeBSD.org
Subject:   [Bug 231129] The ZFS installer sets atime=off by default
Message-ID:  <bug-231129-99-YZ8HqCCFDb@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-231129-99@https.bugs.freebsd.org/bugzilla/>
References:  <bug-231129-99@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D231129

Allan Jude <allanjude@FreeBSD.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |allanjude@FreeBSD.org

--- Comment #1 from Allan Jude <allanjude@FreeBSD.org> ---
There is infact a good reason to disable atime. ZFS is a CoW (Copy-on-Write)
filesystem, so when the atime property is set to on, all snapshots will gro=
w as
the atime attribute of each object is modified. This causes what are suppos=
ed
to be zero-cost snapshots to resume space, and causes read-only workloads to
generate amplification as additional metadata must be read for it to be upd=
ated
to be written out with a modified atime and the checksum of the entire tree=
 of
blocks to be updated.

The 'zfs auto' part of the installer sets atime on ZFS to disabled on purpo=
se,
for all datasets other than /var/mail.

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