On Sat, 6 Aug 2011, Rob Cohen wrote:
Can RAIDZ even do a partial block read? Perhaps it needs to read the full block (from all drives) in order to verify the checksum. If so, then RAIDZ groups would always act like one stripe, unlike RAID5/6.
ZFS does not do partial block reads/writes. It must read the whole block in order to validate the checksum. If there is a checksum failure, then RAID5 type algorithms are used to produce a corrected block.
For this reason, it is wise to make sure that the zfs filesystem blocksize is appropriate for the task, and make sure that the system has sufficient RAM that the zfs ARC can cache enough data that it does not need to re-read from disk for recently accessed files.
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
