Ross Walker wrote:
Raidz is definitely made for sequential IO patterns not random. To get good random IO with raidz you need a zpool with X raidz vdevs where X = desired IOPS/IOPS of single drive.
I have seen statements like this repeated several times, though I haven't been able to find an in-depth discussion of why this is the case. From what I've gathered every block (what is the correct term for this? zio block?) written is spread across the whole raid-z. But in what units? will a 4k write be split into 512 byte writes? And in the opposite direction, every block needs to be read fully, even if only parts of it are being requested, because the checksum needs to be checked? Will the parity be read, too? If this is all the case, I can see why raid-z reduces the performance of an array effectively to one device w.r.t. random reads. Thanks, Arne _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
