[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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