[linux-lvm] Automatic snapshot system?
Heinz J . Mauelshagen
mauelshagen at sistina.com
Mon Dec 3 08:18:02 UTC 2001
On Fri, Nov 30, 2001 at 09:12:53AM -0600, Jason L Tibbitts III wrote:
> >>>>> "JT" == Joe Thornber <thornber at btconnect.com> writes:
> JT> It's a nice idea, but with the current implementation there's no
> JT> way I'd want 100 snapshots of the same origin hanging around.
> They wouldn't all be of the same LV, fortunately; I split my VG up
> into lots of manageable chunks. (Large users get a volume to
> themselves, small users get grouped into various user volumes.) But
> still, I assume that you have some details of performance with the
> current snapshot implementation. Is it that bad?
Well, it does
- copy on write (COW) synchronously *before* et allows the write to
the original LV to proceed
- do multiple reads in case you`ve got multiple snapshots
- does the COWs for multiple snapshots sequentially
This leads to an unecessary read per additional snapshot on the original
LV and therefore to something around n-times delay in case you've got
We will have an asynchrounous implementation which avoids multiple
reads with LVM2.
> - J<
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> linux-lvm at sistina.com
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Heinz -- The LVM Guy --
Heinz Mauelshagen Sistina Software Inc.
Senior Consultant/Developer Am Sonnenhang 11
Mauelshagen at Sistina.com +49 2626 141200
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