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Re: [dm-devel] DM_snapshot_cow filesystem (dmsetup create snapshot)



On 11/30/2011 04:03 PM, Alasdair G Kergon wrote:
On Wed, Nov 30, 2011 at 04:48:05PM -0500, Frederick Grose wrote:
snapshot Invalid  does seem to prevent even read-only access.

Indeed - once it's invalid, that's the end of it.
If we didn't do that, changes to areas of the origin that hadn't already
changed would start to appear in the 'snapshot' and the snapshot would become a
nonsensical hybrid of the two devices containing no information about which
parts of it got corrupted.

Don't allow your snapshots to run out of space!

So wouldn't it be much better as far as the user is concerned if, the instant a snapshot reached capacity, it fell over into a read-only state (instead of being marked invalid?), such that further corruption beyond such plug-pulling variety could/would not occur? If so, would it be straightforward to write such a patch and would it be beneficial enough to end upstream?

-dmc


If you want to see what you can recover, use that code I mentioned earlier.

Alasdair

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