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Re: [Xen-users] Linux Fiber or iSCSI SAN

On Thu, 13 Jun 2013 09:42:54 -0500, Anastas Semenov <anastas.semenov@xxxxxxxxx> wrote:

While 10 drive raidz1 is not most optimal, it is still pretty close to
recommended 4-8 drives.
Perhaps, we are better off going to raidz2.. This is still very much
in evaluation stage.. but so far, we've seen reasonable performance.
More testing required..

Your 10 drive RAIDZ1 might also not be optimal because you effectively have 9 data drives and 1 parity drive. Now I know ZFS doesn't work like normal RAID5/6 semantics and dedicate entire drives to parity, but the concept for how it splits the data and stripes it across the drives can be considered similar. So what you're doing is taking the dataset to be written and dividing it by an odd number (9 chunks + parity).

Now I don't have the ability to point to the code or provide benchmarks at the moment so I'm just parroting what I've been told, but I'm pretty confident you'd get better performance by doing 10 drive RAIDZ2 (data being split into 8 chunks, an even number) or doing 9 drive RAIDZ or 11 drive RAIDZ. In your situation I'd probably go for two 5-drive RAIDZ vdevs if I could afford the loss of storage.

My benchmarks I did when I built my system did seem to mirror the results I was told to expect.

Good luck, and you can never do too much testing!

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