Technology-related ramblings from the edge of the cloud
Friday, 16 March 2007
ZFS and RAID levels
As a builder of Ingres systems, we tend to use RAID 1+0 (aka RAID10) for most of our systems. RAID5 is not recommended for databases due to the read-parity-write that is required for every write operation. Furthermore, the ability of a mirrored system to read two separate data blocks in parallel can give RAID1 a significant read performance advantage.
With the arrival of ZFS in Solaris 10, I've been reading up a little to see if this accepted wisdom changes with RAIDZ. A very interesting article (http://blogs.sun.com/roch/entry/when_to_and_not_
t o) basically explains that the read potential for a RAIDZ filesystem can be significantly less than that of a RAID10. However, for non-data filesystems (such as the checkpoint backup area), RAIDZ can provide some advantages. In these areas, disk I/O is less critical (the Ingres archiver writing data to the journals is performed asynchronously to a users query execution) and sequential write operations are handled better than random I/O, making it ideal for checkpoints and journals, but less good for data areas.