On 9/12/07, Pawel Jakub Dawidek <[EMAIL PROTECTED]> wrote: > On Wed, Sep 12, 2007 at 02:24:56PM -0700, Adam Leventhal wrote: > > On Mon, Sep 10, 2007 at 12:41:24PM +0200, Pawel Jakub Dawidek wrote: > > I'm a bit surprised by these results. Assuming relatively large blocks > > written, RAID-Z and RAID-5 should be laid out on disk very similarly > > resulting in similar read performance. > > Hmm, no. The data was organized very differenly on disks. The smallest > block size used was 2kB, to ensure each block is written to all disks in > RAIDZ configuration. In RAID5 configuration however, 128kB stripe size > was used, which means each block was stored on one disk only. > > Now when you read the data, RAIDZ need to read all disks for each block, > and RAID5 needs to read only one disk for each block. > > > Did you compare the I/O characteristic of both? Was the bottleneck in > > the software or the hardware? > > The bottleneck were definiatelly disks. CPU was like 96% idle. > > To be honest I expected, just like Jeff, much bigger win for RAID5 case.
Well it depends. In both configurations the available read bandwidth is the same. Presumably you're expecting each disk to seek independently and concurrently. Is the spa aware that multiple, offset dependent, reads can be issued concurrently to the RAID-5 vdev? James _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
