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Re: [linux-lvm] Snapshots

Dear John,

On Thu, 17 Sep 2009, Jon Hardcastle wrote:


Do I need some free extents to create a READ ONLY snapshot? I dont have free extents but require a read-only snapshot before doing an upgrade.

Extents are written to the snapshot when changes take place on the volume that the snapshot is based on. If you have no free extents, trying to create a snapshot strikes me as pointless: you may as well mount the origin volume read-only and back up its contents directly (or unmount it and back it up at the level of the volume). Or do you have some special circumstances?

If you make the snapshot read-only, as soon as changes occur on the origin volume the snapshot will become useless: some of the data that are required to make the snapshot usable (i.e. unchanged copies of altered blocks on the origin volume) will no longer exist.


Peter Keller                                     Tel.: +44 (0)1223 353033
Global Phasing Ltd.,                             Fax.: +44 (0)1223 366889
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