On Sun, Jul 6, 2008 at 3:46 PM, Ross <[EMAIL PROTECTED]> wrote: > > For your second one I'm less sure what's going on: > # zpool create temparray raidz c1t2d0 c1t4d0 raidz c1t3d0 c1t5d0 raidz > c1t6d0 c1t8d0 > > This creates three two disk raid-z sets and stripes the data across them. > The problem is that a two disk raid-z makes no sense. Traditionally this > level of raid needs a minimum of three disks to work. I suspect ZFS may be > interpreting raid-z as requiring one parity drive, in which case this will > effectively mirror the drives, but without the read performance boost that > mirroring would give you. > > The way zpool create works is that you can specify raid or mirror sets, but > that if you list a bunch of these one after the other, it simply strips the > data across them. > > I read somewhere, a long time ago when ZFS documentation were still mostly speculation, that raidz will use "mirroring" when the amount of data to be written is less than what justifies 2+parity. Eg in stead of 1+parity, you get mirrored data for small writes, and essentially raid-5 for big writes, with writes with intermediate sizes having raid 5 - like spread of blocks across disks but using fewer than the total nr of disks in the set.
If that still holds true, then a raidz of 2 disks is probably just a mirror?
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