On Mon, 16 Jul 2012, Edward Ned Harvey wrote:

From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of Michael Hase

got some strange results, please see
attachements for exact numbers and pool config:

           seq write  factor   seq read  factor
           MB/sec              MB/sec
single    123        1        135       1
raid0     114        1        249       2
mirror     57        0.5      129       1

I agree with you these look wrong.  Here is what you should expect:

        seq W   seq R
single  1.0     1.0
stripe  2.0     2.0
mirror  1.0     2.0

You have three things wrong:
(a) stripe should write 2x
(b) mirror should write 1x
(c) mirror should read 2x

I would have simply said "for some reason your drives are unable to operate
concurrently" but you have the stripe read 2x.

I cannot think of a single reason that the stripe should be able to read 2x,
and the mirror only 1x.

Yes, I think so too. In the meantime I switched the two disks to another box (hp xw8400, 2 xeon 5150 cpus, 16gb ram). On this machine I did the previous sas tests. OS is now OpenIndiana 151a (vs OpenSolaris b130 before), the mirror pool was upgraded from version 22 to 28, the raid0 pool newly created. The results look quite different:

          seq write  factor   seq read  factor
          MB/sec              MB/sec
raid0     236        2        330       2.5
mirror    111        1        128       1

Now the raid0 case shows excellent performance, the 330 MB/sec are a bit on the optimistic side, maybe some arc cache effects (file size 32gb, 16gb ram). iostat during sequential read shows about 115 MB/sec from each disk, which is great.

The (really desired) mirror case still has a problem with sequential reads. sequential writes to the mirror are twice as fast as before, and show the expected performance for a single disk.

So only one thing left: mirror should read 2x

I suspect the difference is not the hardware, both boxess should have enough horsepower to easily do sequential reads with way more than 200 MB/sec. In all tests cpu time (user and system) remained quite low. I think it's an OS issue: OpenSolaris b130 is over 2 years old, OI 151a dates 11/2011.

Could someone please send me some bonnie++ results for a 2 disk mirror or a 2x2 disk mirror pool with sata disks?


Michael Hase
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