Re: Filesystem snapshots

[Tim Bishop <tim-lists@bishnet.net>]

On Sat, Apr 23, 2016 at 08:03:33PM +0100, John wrote:
> On 04/23/2016 07:22 PM, Graham Percival wrote:
> > What I'm suggesting is this:
> >
> > filesystem RW -+--> (RW, run SQL, emails, etc) ---> filesystem RW
> >                |--> snapshot RO --> run tarsnap --> delete snapshot
> >
> >
> > Essentially, you would not be making your *home directory* read-only.
> > Instead, you could create a read-only copy of your home directory (which
> > continues to be read-write), then you archive that *copy*.
> 
> But the second, it seems to me, requires a partition (or filesystem, or 
> tree portion) to be copied to a large enough temporary space to hold the 
> full dataset which is to be archived, before the next update can be 
> accepted and the backup started side-by-side. If you think it can be 
> achieved without a full data copy being taken while the updates are 
> frozen then this will be a lightbulb-moment for me - continuing to 
> update while creating the copy is no different to updating while backing 
> up, it's just pushing the problem to one remove. I can see how it might 
> be achieved instantly with a mirror dataset, freezing one and continuing 
> to update the other, but we've not discussed those.

Does this help?

http://www.tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html

I've not tried it myself, but that's how I understand CoW filesystems
work and it's as Graham described.

Tim.

-- 
Tim Bishop
http://www.bishnet.net/tim/
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