Hey Tony... When (properly) doing Array-based snapshots/BCVs with EMC/Hitachi/what-have you arrays, you create "lun groups" out of the luns you're interested in snappin'. You then perform snapshot/clone operations on that "lun group" which will make it atomic across all members of that group.
Where things get a lot more interesting is with luns (belonging to the same "snap/clone" group) that live on different arrays. I'm not sure where the vendors are with the concept of federated (still atomic) snapshots, but I suggest avoiding such a configuration entirely thereby side-stepping the issue. My 2 cents, -- MikeE -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Anton B. Rang Sent: Tuesday, September 19, 2006 1:53 PM To: zfs-discuss@opensolaris.org Subject: [zfs-discuss] Re: ZFS and HDS ShadowImage >This isn't true. The snapshot will be entirely consistent - you will >have just lost the last few seconds of non-synchronous writes. Eric, I don't see how this can be the case for a pool backed by multiple LUNs. Take the simple striped case, with two LUNs, 0 and 1. If I take a snapshot of LUN 0 on Monday, and a snapshot of LUN 1 on Tuesday, those two snapshots will not form a consistent ZFS pool. For two snapshots taken only a second apart, there's more chance that they will be consistent, but it's still not guaranteed. I'm not sure whether HDS allows a snapshot of multiple LUNs to be taken atomically, which is required to take a consistent snapshot of a multi-LUN file system like ZFS or QFS (or, for that matter, UFS over SVM). For UFS, 'lockfs -w' allows consistency. QFS is missing this. I don't think it's implemented for ZFS yet either, though it seems it would be fairly simple to implement (simply pause after the current transaction group and don't start another; perhaps writes to the intent log should be paused as well). Anton This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
