> From: opensolaris-discuss-boun...@opensolaris.org [mailto:opensolaris- > discuss-boun...@opensolaris.org] On Behalf Of Dmitry G. Kozhinov > > > I need to know exactly when the snapshot gets committed to the disk so I > can backup my disk. > > You access your disk (for backup purpose) via operating system. The OS will > show you the disk in the logical state in which it got after all write operations, > regardless of whether they were physically completed or not.
Dmitry, you've assumed too much - Justin might be correct. If you backup your filesystem from inside the OS, then Dmitry is correct. You don't have to worry about whether it's immediately synced or not, because inside the OS, all access to the zpool will use the in-memory data structures. But if you have enterprise storage, and you're backing up your storage through a 3rd party command issued to the storage controller at a level below what ZFS sees... Then it's conceivable you might care about the snapshot operation being asynchronous versus synchronous. So, Justin, a few more comments: Suppose you issue "zfs snapshot" command, and suppose it's async. Meaning it's not yet written to disk. And you then "snapshot" the storage using an enterprise low-level storage device command. Then your hardware snapshot will not include the zfs snapshot inside of it, but maybe you don't care. Under no circumstance does ZFS write an inconsistent filesystem to disk, which means, any hardware snapshot you create will service functionally just as well as the software snapshot. If you are doing a hardware snapshot, then the only reason you care about zfs snapshot being sync or async... If you want a convenient label inside your hardware snapshot to indicate when it was taken. So, all that being said... Do you still care? I am surprised nobody has actually answered the question yet. You're asking in the right place. Somebody here definitely knows the answer. When you "zfs snapshot" a filesystem, is that a sync operation, or async? Does the snapshot creation happen in ZIL before it gets flushed to main storage? _______________________________________________ opensolaris-discuss mailing list opensolaris-discuss@opensolaris.org
