[linux-lvm] Snapshot behavior on classic LVM vs ThinLVM

Stuart D. Gathman stuart at gathman.org
Tue Apr 18 14:32:34 UTC 2017

On Tue, 18 Apr 2017, Gionatan Danti wrote:

> Any thoughts on the original question? For snapshot with relatively big CoW 
> table, from a stability standpoint, how do you feel about classical vs 
> thin-pool snapshot?

Classic snapshots are rock solid.  There is no risk to the origin
volume.  If the snapshot CoW fills up, all reads and all writes to the
*snapshot* return IOError.  The origin is unaffected.

If a classic snapshot exists across a reboot, then the entire CoW table
(but not the data chunks) must be loaded into memory when the snapshot 
(or origin) is activated.  This can greatly delay boot for a large CoW.

For the common purpose of temporary snapsnots for consistent backups,
this is not an issue.

 	      Stuart D. Gathman <stuart at gathman.org>
"Confutatis maledictis, flamis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

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