On Wed, Jun 10, 2009 at 14:18, Clayton Wheeler<[email protected]> wrote: > I'm setting up OpenSolaris on Amazon EC2, and planning on using their Elastic > Block Store volumes to store a persistent ZFS zpool. I'm inclined to make a > mirror of two EBS volumes (essentially LUNs with snapshot features and an API > for mapping/unmapping them), for better data protection. However, EC2 only > lets you snapshot one volume at a time; there is no consistency group feature > for taking simultaneous snapshots of the volumes comprising a zpool. > Likewise, you can only map or unmap one volume at a time. You could export the zpool (which will cause it to stop writing to disk) and then take the snapshots. This would prevent desynchronized volumes entirely.
> My question is this: how well can ZFS deal with the mirror devices getting > out of sync? For instance, if one or both of my EBS volumes are lost and I > have to restore from EBS snapshots, one volume will have a newer version of > the data than the other. Will ZFS be able to recognize this and safely > resilver from the newer device to the older? In my experience, ZFS doesn't have problems with this kind of scenario as long as you don't touch the snapshots before feeding both of them back into the system. That is, if you snapshot volumes A and B at different times, don't make changes to both (producing A' and B') before putting them back in a zpool. A and B will be able to form a mirror, but A' and B' will not necessarily. You should make sure that whatever application you are running forces sync of its data to disk before taking the snapshots, but you probably knew that already. Will _______________________________________________ zfs-discuss mailing list [email protected] http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
