[linux-lvm] Snapshots and disk re-use
Stuart D. Gathman
stuart at bmsi.com
Wed Feb 23 20:37:20 UTC 2011
On Wed, 23 Feb 2011, Les Mikesell wrote:
> Which is why re-writing stuff that was already correct and not being modified
> doesn't make much sense.
So set the origin to readonly.
> > Writes to the snapshot, on the other hand, simply write to the *-cow with
> > some mapping, no need to update the origin.
> I would have guessed that snapshots were read-only. If you can write, it isn't
> really a snapshot, is it?
So set the snapshot to readonly.
But to be useful, you need to write to one or the other. Using the origin as a
(mostly) readonly "template" for many VM customers works efficiently with VMs
running in snapshots. In that case, writes to the snapshots are just one
write. You *could* consider the origin a "snapshot" in that case. But then
you are defining "snapshot" to be the readonly branch, which is a different
sense than how LVM uses the term.
Stuart D. Gathman <stuart at bmsi.com>
Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.
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