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Re: [linux-lvm] snapshotting to a different volume group



2008-04-18 12:53:15 +0100, Stephane Chazelas:
[...]
> By bypassing LVM2 and using dmsetup directly, would I
> theoretically be able to setup a snapshot outside of LVM2
> managed volume groups, is it worth me trying to dig that way?
> Something like: having a LVM (or not) volume group with only
> /dev/md0 and creating snapshots of that elsewhere while leaving
> the VG containing /dev/md0 undisturbed?
[...]

[replying to myself]

OK, I get it.

When one creates a snapshot, he changes the original block
device to be a "snapshot-origin" so that every write to the
device is forked into:
  - copying the original block to the snapshot device(s) COW(s)
  - writing to the original device.

So, if I've got the COWs on a failed disk, I suspect this might
degrade the performances or even stop the snapshot-origin from
working altogether wouldn't it?

I'll keep testing...

-- 
Stephane


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