On 29 November 2010 15:03, Erik Trimble <erik.trim...@oracle.com> wrote:
> I'd have to re-look at the ZFS Best Practices Guide, but I'm pretty sure > the recommendation of 7, 9, or 11 disks was for a raidz1, NOT a raidz2. Due > to #5 above, best performance comes with an EVEN number of data disks in any > raidZ, so a write to any disks is always a full portion of the chunk, rather > than a partial one (that sounds funny, but trust me). The best balance of > size, IOPs, and throughput is found in the mid-size raidZ(n) configs, where > there are 4, 6 or 8 data disks. > Let the maximum block size of 128KiB = s If the number of disks in a raidz vdev = n, p = number of parity disks used and d = data drives. Hence, n = d + p So, for some given numbers of d: d s/d 1 128 2 64 3 42.67 4 32 5 25.6 6 21.33 7 18.29 8 16 9 14.22 10 12.8 Hence, for a raidz vdev with a width of 7, d = 6; s/d = 21.33KiB. This isn't an ideal block size by any stretch of the imagination. Same thing for a width of 11, d = 10, s/d = 12.8KiB. What you were aiming for: for ideal performance, one should keep the vdev width to the form 2^x + p. So, for raidz: 2, 3, 5, 9, 17. raidz2: 3, 4, 6, 10, 18, etc. Cheers,
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