On May 19, 2009, at 12:57 PM, Dave wrote:
If you don't have mirrored slogs and the slog fails, you may lose any data that was in a txg group waiting to be committed to the main pool vdevs - you will never know if you lost any data or not.
None of the above is correct. First off, you only lose data if the slog fails *and* the machine panics/reboots before the transaction groups is synced (5-30s by default depending on load, though there is a CR filed to immediately sync on slog failure). You will not lose any data once the txg is synced - syncing the transaction group does not require reading from the slog, so failure of the log device does not impact normal operation.
The latter half of the above statement is also incorrect. Should you find yourself in the double-failure described above, you will get an FMA fault that describes the nature of the problem and the implications. If the slog is truly dead, you can 'zpool clear' (or 'fmadm repair') the fault and use whatever data you still have in the pool. If the slog is just missing, you can insert it and continue without losing data. In no cases will ZFS silently continue without committed data.
- Eric -- Eric Schrock, Fishworks http://blogs.sun.com/eschrock _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
