Jim Dunham wrote: > David, > >> Hello, >> >> We're trying to implement snapshots on iSCSI volumes using Open >> Solaris v.10 + ZFS. On the first attempt, snapshot was taken during >> file transfer. It seems as though there's no synchronization done by >> snapshot so as to flush the cache that's being queued in the memory >> before taking the snapshot. Result was corruped snapshot. > > Can you share some configuration information for iSCSI, ZFS storage > pools, and the ZFS filesystem being snapped. Then those steps done to > take the snapshot, and later the error messages showing that the > snapshot was indeed corrupted. > > If you were to read the low-level details on how snapshot are > implemented internally in ZFS, I would question that the snapshot was > corrupted, but instead that the snapshot was taken while ZFS > filesystem I/Os were in-flight. There are key difference between ZFS > on-disk consistency, and application on-file consistency, something > driven by POSIX filesystem semantics.
I too am curious what the config is.... let me drop some hints: 1) ZFS is always consistent on disk (as Jim said). 2) Snapshots are an inherent consequence of the Copy-on-Write design of ZFS. Snapshots are NOT a bolt on feature. 3) When iSCSI is involved you must bear in mind that while that your dealing with 2 filesystems. If you run UFS or ext3 or whatever on an iSCSI LUN from a ZFS Volume, and you don't cleanly unmount filesystem prior to snapshot you're going to end up with a filesystem that needs to be fsck'ed (at least) when you try to use that FS again. My guess is that the ZFS data structure isn't corrupt, but that the filesystem within the ZFS Volume is. Thats not ZFS's fault. Remember, when snapshoting iSCSI LUNs its equivalent to pulling the drive out of a system. If its running the disks are gonna be inconsistent.... not corrupt, but inconsistent. If you must do this make sure you've got a really good logging filesystem on the iSCSI client/initiator side. >> Is there a way to make snapshot function properly in iSCSI environment? > > Why do you think that this is an iSCSI issue? Agreed, this is not an iSCSI issue. benr. _______________________________________________ storage-discuss mailing list [email protected] http://mail.opensolaris.org/mailman/listinfo/storage-discuss
