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Re: Is xfsdump operation atomic?

To: linux-xfs@xxxxxxxxxxx
Subject: Re: Is xfsdump operation atomic?
From: Ivan Rayner <ivanr@xxxxxxx>
Date: Wed, 24 Nov 2004 10:08:27 +1100
In-reply-to: <81DB11CE-3D40-11D9-B9BB-000A95BCCB96@xxxxxxxxxxxx>
Organization: SGI
References: <81DB11CE-3D40-11D9-B9BB-000A95BCCB96@xxxxxxxxxxxx>
Sender: linux-xfs-bounce@xxxxxxxxxxx
On Tue, 23 Nov 2004 12:12:04 +0100, Michael Locher wrote:

> I wonder if xfsdump is an atomic operation

No it isn't.

> and thus can be savely used on a live filesystem?

Yes it can.  In fact it can _only_ be run on a live filesystem.

> If not, what is the recommended way to backup a live XFS filesystem?

Whatever you like that suits your needs.  xfsdump is suitable for many
but there are many options from commercial backup programs like Legato
Networker to things like tar & cpio.

> I guess this information would also be interessting to others, so why 
> not include it in the paragraph about xfsdump on the XFS homepage?

I'm sure the man page states that it should be run on a mounted
filesystem.

You seem to be of the opinion that you can't create a backup of a live
filesystem.  My guess is that you assume a backup is a strict snapshot in
time of the filesystem -- it isn't.

If a file is removed or created while a xfsdump is running, then it may or
may not be included in the dump.  This is OK, because in tomorrow night's
incremental backup the file will then be included or removed as
appropriate.  If you have a 24hr schedule then you should assume that the
cycle starts when xfsdump starts.  Anything that happens while xfsdump is
running will be guaranteed to be on the following dump, but if you're
lucky then it will make it in the current dump.

If you really want to create a full dump, then just make sure filesystem
is not in use, by un-exporting it via nfs or mounting it on another mount
point, or stop users logging in, or scheduling it for 3am, or whatever...

Ivan


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