On Thu, 14 Jan 2010, Jeffry Molanus wrote:
Are there any recommendations regarding min IOPS the backing storage pool needs to have when flushing the SSD ZIL to the pool? Consider a pool of 3x 2TB SATA disks in RAIZ1, you would roughly have 80 IOPS. Any info about the relation between ZIL <> pool performance? Or will the ZIL simply fill up and performance drops to pool speed?
There are different kinds of "IOPS". The expensive ones are random IOPS whereas sequential IOPS are much more efficient. The intention of the SSD-based ZIL is to defer the physical write so that would-be random IOPS can be converted to sequential scheduled IOPS like a normal write. ZFS coalesces multiple individual writes into larger sequential requests for the disk.
Regardless, some random access to the underlying disks is still required. If the pool becomes close to full (or has become fragmented due to past activities) then there will be much more random access and the SSD-based ZIL will not be as effective.
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
