On Jul 20, 2010, at 3:46 AM, Roy Sigurd Karlsbakk wrote: > ----- Original Message ----- >> Hi, >> for zfs raidz1, I know for random io, iops of a raidz1 vdev eqaul to >> one physical disk iops, since raidz1 is like raid5 , so is raid5 has >> same performance like raidz1? ie. random iops equal to one physical >> disk's ipos. > > Mostly, yes. Traditionl RAID-5 is likely to be faster than ZFS because of ZFS > doing checksumming, having the ZIL etc, but then, trad raid5 won't have the > safety offered by ZFS
Disagree. ZIL has nothing to do with RAIDness. Traditional RAID-5 suffers from a read-modify-write sequence if the I/O is not perfectly matched to the stripe width -- a 3x latency hit. In raidz, the writes are always full stripe, so there is only a 1x latency hit. OTOH, for reads, some RAID-5 implementations will read only a single portion of a stripe, if the I/O is small enough to fit. In this case, the small, random read performance can approach RAID-0. raidz will always read the full block, even though the full block might not be spread across all of the disks. ZFS does this to verify the checksum of the data. This is the classic tradeoff -- space, performance, dependability: pick two. -- richard -- Richard Elling rich...@nexenta.com +1-760-896-4422 Enterprise class storage for everyone www.nexenta.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
