>If you have an ungraceful shutdown in the middle of writing stuff, while the >ZIL is disabled, then you have corrupt data. Could be files that are >partially written. Could be wrong permissions or attributes on files. >Could be missing files or directories. Or some other problem. > >Some changes from the last 1 second of operation before crash might be >written, while some changes from the last 4 seconds might be still >unwritten. This is data corruption, which could be worse than losing a few >minutes of changes. At least, if you rollback, you know the data is >consistent, and you know what you lost. You won't continue having more >losses afterward caused by inconsistent data on disk.
How exactly is this different from "rolling back to some other point of time?". I think you don't quite understand how ZFS works; all operations are grouped in transaction groups; all the transactions in a particular group are commit in one operation. I don't know what partial ordering ZFS uses when creating transaction groups, but a snapshot just picks one transaction group as the last group included in the snapshot. When the system reboots, ZFS picks the most recent, valid uberblock; so the data available is "correct upto transaction group N1". If you rollback to a snapshot, you get data "correct upto transaction group N2". But N2 < N1 so you lose more data. Why do you think that a "Snapshot" has a "better quality" than the last snapshot available? Casper _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
