> It's just a common sense advise - for many users keeping raidz groups > below 9 disks should give good enough performance. However if someone > creates raidz group of 48 disks he/she probable expects also > performance and in general raid-z wouldn't offer one.
There is at least one reason for wanting more drives in the same raidz/raid5/etc: redundancy. Suppose you have 18 drives. Having two raidz:s constisting of 9 drives is going to mean you are more likaly to fail than having a single raidz2 consisting of 18 drives, since in the former case yes - two drives can go down, but only if they are the *right* two drives. In the latter case any two drives can go down. The ZFS administration guide mentions this recommendation, but does not give any hint as to why. A reader may assume/believe it's just general adviced, based on someone's opinion that with more than 9 drives, the statistical probability of failure is too high for raidz (or raid5). It's a shame the statement in the guide is not further qualified to actually explain that there is a concrete issue at play. (I haven't looked into the archives to find the previously mentioned discussion.) -- / Peter Schuller, InfiDyne Technologies HB PGP userID: 0xE9758B7D or 'Peter Schuller <[EMAIL PROTECTED]>' Key retrieval: Send an E-Mail to [EMAIL PROTECTED] E-Mail: [EMAIL PROTECTED] Web: http://www.scode.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
