[linux-lvm] Snapshots and disk re-use

Stuart D. Gathman stuart at bmsi.com
Thu Feb 24 15:13:00 UTC 2011

On Thu, 24 Feb 2011, Jonathan Tripathy wrote:

> > Yes. To be more pedantic, the COW has copies of the original contents
> > of blocks written to the origin since the snapshot.  That is why you
> > need to clear it to achieve your stated purpose.  The origin blocks
> > are written normally to the *-real volume (you can see these in
> > the /dev/mapper directory).
> But didn't you say that there is only one copy of the files stored physically
> on disk?

Yes.  When you make the snapshot, there is only one copy, and the COW table
is empty.  AS YOU WRITE to the origin, each chunk written is saved to
*-cow first before being written to *-real.

	      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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