From: Gionatan Danti <g.danti@assyoma.it>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, g.danti@assyoma.it
Subject: Re: Reflink (cow) copy of busy files
Date: Sat, 24 Feb 2018 23:57:32 +0100 [thread overview]
Message-ID: <711dd96e3c4b3e92d3fb38a01e77dc64@assyoma.it> (raw)
In-Reply-To: <20180224220757.GC30854@dastard>
Il 24-02-2018 23:07 Dave Chinner ha scritto:
> Define "busy file", please.
Think about a running virtual machine. Maybe an XFS-based virtual image
(ie: a CentOS 7 guest).
> If the file is being actively written, then the clone will not be
> consistent.
>
> Yes, it's just like any other snapshot process - you have to quiesce
> everything that is writing to the file before cloning it. i.e. the
> data in the file needs to be in a stable, consistent, unchanging
> state if you want the clone to contain consistent data...
About *what* level of consistency are we speaking? I understand that
application-level consistency requires a quiesced filesystem and,
possibly, an application-level agent. But is it a quiesced filesystem a
requisite for a *crash-consistent* ie: pull the plug) snapshot?
In other words: would a cp --reflink=always <vmdisk> <snapshot> of a
runnig virtual machine produce an usable, crash-consistent snapshot, or
it risks ending with binary garbage?
Thanks.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
next prev parent reply other threads:[~2018-02-24 22:57 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-24 18:20 Reflink (cow) copy of busy files Gionatan Danti
2018-02-24 22:07 ` Dave Chinner
2018-02-24 22:57 ` Gionatan Danti [this message]
2018-02-25 2:47 ` Dave Chinner
2018-02-25 11:40 ` Gionatan Danti
2018-02-25 21:13 ` Dave Chinner
2018-02-25 21:58 ` Gionatan Danti
2018-02-26 0:25 ` Dave Chinner
2018-02-26 7:19 ` Gionatan Danti
2018-02-26 7:58 ` Amir Goldstein
2018-02-26 8:26 ` Gionatan Danti
2018-02-26 17:26 ` Darrick J. Wong
2018-02-26 21:23 ` Gionatan Danti
2018-02-26 21:31 ` Darrick J. Wong
2018-02-26 21:39 ` Gionatan Danti
2018-02-27 0:33 ` Dave Chinner
2018-02-27 0:58 ` Darrick J. Wong
2018-02-27 8:06 ` Gionatan Danti
2018-02-27 22:04 ` Dave Chinner
2018-02-28 7:08 ` Gionatan Danti
2018-02-28 17:07 ` Darrick J. Wong
2018-02-28 18:27 ` Gionatan Danti
2018-02-26 20:29 ` Amir Goldstein
2018-02-26 21:28 ` Gionatan Danti
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