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Re: Snapshots

To: Greg Freemyer <freemyer@xxxxxxxxxxxxxxxxx>
Subject: Re: Snapshots
From: Seth Mos <knuffie@xxxxxxxxx>
Date: Thu, 2 May 2002 19:07:36 +0200 (CEST)
Cc: <linux-xfs@xxxxxxxxxxx>
In-reply-to: <20020502165502.BNSV7141.imf00bis.bellsouth.net@taz>
Sender: owner-linux-xfs@xxxxxxxxxxx
On Thu, 2 May 2002, Greg Freemyer wrote:

> XFS team,
> I've just become aware of a problem on another Journaled file-system (it is 
> not a Linux filesystem).

A NAS device perhaps?

> With this filesystem, the meta-data can be out of sync during a snapshot 
> operation.
> If this happens, the snapshot is corrupt and can't be counted on to be a 
> valid backup.
> They are introducing a new feature for it: "freeze/thaw".
> The idea is that you issue a freeze prior to taking the snapshot and a thaw 
> after the snapshot is complete.
> Does XFS have any similar problems, and if so are there fixes in place, or in 
> the pipeline.
> Note that this was a very occasional problem on the other filesystem, so 
> anecdotal statements of it "works fine for me" may not mean much.

AFAIK XFS has a freeze/thaw operation and some others are using it
together with LVM to create snapshots of filesystems.

I have no idea how heavy this is used out there but we do see the
occasional message fly by.

You can find more user experiences with respect to snapshots using the
mailinglist archive.

Maybe others will chime in as well.


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