> > http://blogs.sun.com/roller/page/roch?entry=when_to_and_not_to > > thanks, that is very useful information. it pretty much rules out raid-z > for this workload with any reasonable configuration I can dream up > with only 12 disks available. it looks like mirroring is going to > provide higher write IOPS and increased redundancy, obviously at the > expense of the available space.
There's an important caveat I want to add to this. When you're doing sequential I/Os, or have a write-mostly workload, the issues that Roch explained so clearly won't come into play. The trade-off between space-efficient RAID-Z and IOP-efficient mirroring only exists when you're doing lots of small random reads. If your I/Os are large, sequential, or write-mostly, then ZFS's I/O scheduler will aggregate them in such a way that you'll get very efficient use of the disks regardless of the data replication model. It's only when you're doing small random reads that the difference between RAID-Z and mirroring becomes significant. For such workloads, everything that Roch said is spot on. Jeff _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
