On Tue, Sep 19, 2006 at 10:52:52AM -0700, Anton B. Rang wrote: > > 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).
Ah. I has assumed that 'taking a LUN snapshot' was an atomic operation across all LUNs in the pool. If this isn't possible, then you are correct - you can easily end up with inconsistent and corrupted state. Taking a snapshot of a single LUN pool will not lead to inconsistency. - Eric -- Eric Schrock, Solaris Kernel Development http://blogs.sun.com/eschrock _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
