On Tue, 22 Dec 2009, Marty Scholes wrote:
If there is a RAIDZ write penalty over mirroring, I am unaware of it. In fact, sequential writes are faster under RAIDZ.
There is always an IOPS penalty for raidz when writing or reading, given a particular zfs block size. There may be a write penalty for mirroring, but this depends heavily on whether the I/O paths are saturated or operate in parallel. It is true that a mirror requires a write for each mirror device, but if the I/O subsystem has the bandwidth for it, the cost of this can be astonishingly insignificant. It becomes significant when the I/O path is shared with limited bandwidth and the writes are large.
As to whether sequential writes are faster under raidz, I have yet to see any actual evidence of that. Perhaps someone can provide some actual evidence?
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
