On Wed, 7 Apr 2010, Chris Dunbar wrote:
More for my own edification than to help Jason (sorry Jason!) I would like to clarify something. If read performance is paramount, am I correct in thinking RAIDZ is not the best way to go? Would not the ZFS equivalent of RAID 10 (striped mirror sets) offer better read performance? In this case, I realize that Jason also needs to
Striped mirror vdevs are assured to offer peak performance. One would (naively) think that the striping in a raidz2 would allow it to offer more sequential performance, but zfs's sequential file prefetch allows mirrors to offer about the same level of sequential performance. With the mirror setup, 128K blocks are pulled from each disk whereas with the raidz setup, the 128K block is split across the drives constituting a vdev. Zfs is very good at ramping up prefetch for large sequential files. Due to this, raidz2 should be seen as a way to improve storage efficiency and data reliability, and not so much as a way to improve sequential performance.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, 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
