Bart Smaalders wrote: > michael T sedwick wrote: >> Given a 1.6TB ZFS Z-Raid consisting 6 disks: >> And a system that does an extreme amount of small /(<20K) /random >> reads /(more than twice as many reads as writes) / >> >> 1) What performance gains, if any does Z-Raid offer over other RAID >> or Large filesystem configurations? >> >> 2) What is any hindrance is Z-Raid to this configuration, given the >> complete randomness and size of these accesses? >> >> >> Would there be a better means of configuring a ZFS environment for >> this type of activity? >> >> thanks; >> > > A 6 disk raidz set is not optimal for random reads, since each disk in > the raidz set needs to be accessed to retrieve each item. Note that if > the reads are single threaded, this doesn't apply. However, if multiple > reads are extant at the same time, configuring the disks as 2 sets of > 3 disk raidz vdevs or 3 pairs of mirrored disk will result in 2x and 3x > (approx) total parallel random read throughput. > I'm not sure why, but when I was testing various configurations with bonnie++, 3 pairs of mirrors did give about 3x the random read performance of a 6 disk raidz, but with 4 pairs, the random read performance dropped by 50%:
3x2 Block read: 220464 Random read: 1520.1 4x2 Block read: 295747 Random read: 765.3 Ian _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
