> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of MLR > > Say we get a decent ssd, ~500MB/s read/write. If we have a 20 HDD zpool > setup shouldn't we be reading at least at the 500MB/s read/write range? > Why > would we want a ~500MB/s cache?
You don't add l2arc because you care about MB/sec. You add it because you care about IOPS (read). Similarly, you don't add dedicated log device for MB/sec. You add it for IOPS (sync write). Any pool - raidz, raidz2, mirror - will give you optimum *sequential* throughput. All the performance enhancements are for random IO. Mirrors outperform raidzN, but in either case, you get improvements by adding log & cache. > Am I correct in > thinking this means, for example, I have a single 14 disk raidz2 vdev zpool, It's not advisable to put more than ~8 disks in a single vdev, because it really hurts during resilver time. Maybe a week or two to resilver like that. > the > disks will go ~100MB/s each , this zpool would theoretically read/write at No matter which configuration you choose, you can expect optimum throughput from all drives in sequential operations. Random IO is a different story. > What would be the best setup? I'm thinking one of the following: > a. 1vdev of 8 1.5TB disks (raidz2). 1vdev of 12 3TB disks (raidz3)? > (~200MB/s reading, best reliability) No. 12 in a single vdev is too much. > b. 1vdev of 8 1.5TB disks (raidz2). 3vdev of 4 3TB disks (raidz)? (~400MB/s > reading, evens out size across vdevs) Not bad, but different size vdev's will perform differently (8 disks vs 4) so... See below. > c. 2vdev of 4 1.5TB disks (raidz). 3vdev of 4 3TB disks (raidz)? (~500MB/s > reading, maximize vdevs for performance) This would be your optimal configuration. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
