On Apr 15, 2008, at 13:18, Bob Friesenhahn wrote: > ZFS raidz1 and raidz2 are NOT directly equivalent to RAID5 and RAID6 > so the failure statistics would be different. Regardless, single disk > failure in a raidz1 substantially increases the risk that something > won't be recoverable if there is a media failure while rebuilding. > Since ZFS duplicates its own metadata blocks, it is most likely that > some user data would be lost but the pool would otherwise recover. If > a second disk drive completely fails, then you are toast with raidz1. > > RAID5 and RAID6 rebuild the entire disk while raidz1 and raidz2 only > rebuild existing data blocks so raidz1 and raidz2 are less likely to > experience media failure if the pool is not full.
While the failure statistics may be different, I think any comparison would be "apples-to-apples". RAID-5/6 would be the "worst case", with ZFS having slightly better numbers; it having a slight advantage because of checksuming (to head reduce the chance of undetected / unrecoverable read errors) and because you're only recreating used blocks instead of all blocks (less stress on the disks; shorter rebuild time). There's also the consistency advantage (no fsck time; no write hole). In general you could probably calculate the numbers for RAID-5/6, and be fairly comfortable thinking that RAID-Z/2 is better than whatever you get. (For some quantity of "better".) _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
