On Fri, 18 Apr 2008, Pascal Vandeputte wrote: > Thanks for all the replies! > > Some output from "iostat -x 1" while doing a dd of /dev/zero to a > file on a raidz of c1t0d0s3, c1t1d0 and c1t2d0 using bs=1048576: [ data removed ] > It's all a little fishy, and kw/s doesn't differ much between the > drives (but this could be explained as drive(s) with longer wait > queues holding back the others I guess?).
Your data does strongly support my hypothesis that using a slice on 'sd0' would slow down writes. It may also be that your boot drive is a different type and vintage from the other drives. Testing with output from /dev/zero is not very good since zfs treats blocks of zeros specially. I have found 'iozone' (http://www.iozone.org/) to be quite useful for basic filesystem throughput testing. > Hmm, doesn't look like one drive holding back another one, all of > them seem to be equally slow at writing. Note that if drives are paired, or raidz requires a write to all drives, then the write rate is necessarily limited to the speed of the slowest device. I suspect that your c1t1d0 and c1t2d0 drives are similar type and vintage whereas the boot drive was delivered with the computer and has different performance characteristics (double wammy). Usually drives delivered with computers are selected by the computer vendor based on lowest cost in order to decrease the cost of the entire computer. SATA drives are cheap this days so perhaps you can find a way to add a fourth drive which is at least as good as the drives you are using for c1t1d0 and c1t2d0. Bob ====================================== Bob Friesenhahn [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
