On 31/03/2010 17:22, Edward Ned Harvey wrote:
The advice I would give is: Do zfs autosnapshots frequently (say ... every 5 minutes, keeping the most recent 2 hours of snaps) and then run with no ZIL. If you have an ungraceful shutdown or reboot, rollback to the latest snapshot ... and rollback once more for good measure. As long as you can afford to risk 5-10 minutes of the most recent work after a crash, then you can get a 10x performance boost most of the time, and no risk of the aforementioned data corruption.
I don't really get it - rolling back to a last snapshot doesn't really improve things here it actually makes it worse as now you are going to loose even more data. Keep in mind that currently the maximum time after which ZFS commits a transaction is 30s - ZIL or not. So with disabled ZIL in worst case scenario you should loose no more than last 30-60s. You can tune it down if you want. Rolling back to a snapshot will only make it worse. Then also keep in mind that it is a worst case scenario here - it well may be there were no outstanding transactions at all - it all goes down basically to a risk assessment, impact assessment and a cost.
Unless you are talking about doing regular snapshots and making sure that application is consistent while doing so - for example putting all Oracle tablespaces in a hot backup mode and taking a snapshot... otherwise it doesn't really make sense.
-- Robert Milkowski http://milek.blogspot.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
