Another issue with all this arithmetic: one needs to factor in the cost of additional spare disks (what were you going to resilver onto?).
I look at it like this: you purchase the same number of total disks (active + hot spare + cold spare), and raidz2 vs raidz3 simply moves a disk from one of the spare columns to the active column. Raidz3 gives you longer to find (potentially even purchase, at future cheaper prices) the replacement disk, which might simply be a replacement cold spare. On Sun, Jan 24, 2010 at 12:20:37PM -0500, Frank Cusack wrote: > But you'd do even better to use a triple mirror of the > smaller drives. By R.G's now well-stated and clear objectives and criteria for "better", no. He'd need at least a 4-way mirror, to survive 3 faults. Sorry to nit-pick your arithmetic again :) Assuming 4 active disks total (for capital cost equivalence), when it comes to other criteria, like random-IOPS, most of use would prefer the mirror, of those two configs. If those criteria are not as important to you, there may still be reasons to prefer raidz3, perhaps because different data patterns are written to each disk, protecting you against some potential data-sensitive deficiency in the on-disk error recovery. If you want any more than 3 faults, your only choice is mirrors (for now). By - or even well before - that stage, you should be looking at off-site replication. -- Dan.
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