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Date: Thu, 24 Feb 2011 15:20:35 +0000
From: Jonathan Tripathy <jonnyt@abpni.co.uk>
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Subject: Re: [linux-lvm] Snapshots and disk re-use
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On 24/02/11 15:13, Stuart D. Gathman wrote:
> 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 physi=
cally
>> on disk?
> Yes.  When you make the snapshot, there is only one copy, and the COW tab=
le
> is empty.  AS YOU WRITE to the origin, each chunk written is saved to
> *-cow first before being written to *-real.
Got ya. So data that is being written to the origin, while the snapshot=20
exists, is the data that may leak, as it's saved to the COW first, then=20
copied over to real.

Hopefully an expert will let me know weather its safe to zero the COW=20
after I=EF=BF=BDve finished with the snapshot.