On Thu, 20 Aug 2009, Tristan Ball wrote:
I believe you will actually get the read IOP's rate of 4 disks, rather than 8. ZFS doesn't load balance reads accross mirrrors like raid does, rather it reads from both mirrors so it can compare checksums.
Why would zfs want to read from both mirror devices so that it can compare checksums? That is useless work which does not make any sense at all.
It may be that zfs does not carefully balance reads across mirrors but it does do non-preferential load-balanced reads using either device in the pair. Statistically this results in measurable benefit. Someday maybe zfs will become smarter and carefully direct the I/O requests for more benefit with mirrors.
But happy to be shown wrong if someone can provider references? :-)
Smoking Mirrors! Bob -- Bob Friesenhahn [email protected], http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ storage-discuss mailing list [email protected] http://mail.opensolaris.org/mailman/listinfo/storage-discuss
