Re: Intel SSDs that may not suck

On Mar 29, 2011, at 10:16 AM, Jeff wrote:

> Now that all sounds awful and horrible until you get to overall
> performance, especially with reads - you are looking at 20k random
> reads per second with a few disks. Adding in writes does kick it
> down a noch, but you're still looking at 10k+ iops. That is the
> current trade off.
>

We've been doing a burn in for about 4 days now on an array of 8
x25m's behind a p812 controller: here's a sample of what it is
currently doing (I have 10 threads randomly seeking, reading, and 10%
of the time writing (then fsync'ing) out, using my pgiosim tool which
I need to update on pgfoundry)

10:25:24 AM dev104-2 7652.21 109734.51 12375.22 15.96
8.22 1.07 0.12 88.32
10:25:25 AM dev104-2 7318.52 104948.15 11696.30 15.94
8.62 1.17 0.13 92.50
10:25:26 AM dev104-2 7871.56 112572.48 13034.86 15.96
8.60 1.09 0.12 91.38
10:25:27 AM dev104-2 7869.72 111955.96 13592.66 15.95
8.65 1.10 0.12 91.65
10:25:28 AM dev104-2 7859.41 111920.79 13560.40 15.97
9.32 1.19 0.13 98.91
10:25:29 AM dev104-2 7285.19 104133.33 12000.00 15.94
8.08 1.11 0.13 92.59
10:25:30 AM dev104-2 8017.27 114581.82 13250.91 15.94
8.48 1.06 0.11 90.36
10:25:31 AM dev104-2 8392.45 120030.19 13924.53 15.96
8.90 1.06 0.11 94.34
10:25:32 AM dev104-2 10173.86 145836.36 16409.09 15.95
10.72 1.05 0.11 113.52
10:25:33 AM dev104-2 7007.14 100107.94 11688.89 15.95
7.39 1.06 0.11 79.29
10:25:34 AM dev104-2 8043.27 115076.92 13192.31 15.95
9.09 1.13 0.12 96.15
10:25:35 AM dev104-2 7409.09 104290.91 13774.55 15.94
8.62 1.16 0.12 90.55

the 2nd to last column is svctime. first column after dev104-2 is
TPS. if I kill the writes off, tps rises quite a bit:
10:26:34 AM dev104-2 22659.41 361528.71 0.00 15.95
10.57 0.42 0.04 99.01
10:26:35 AM dev104-2 22479.41 359184.31 7.84 15.98
9.61 0.52 0.04 98.04
10:26:36 AM dev104-2 21734.29 347230.48 0.00 15.98
9.30 0.43 0.04 95.33
10:26:37 AM dev104-2 21551.46 344023.30 116.50 15.97
9.56 0.44 0.05 97.09
10:26:38 AM dev104-2 21964.42 350592.31 0.00 15.96
10.25 0.42 0.04 96.15
10:26:39 AM dev104-2 22512.75 359294.12 7.84 15.96
10.23 0.50 0.04 98.04
10:26:40 AM dev104-2 22373.53 357725.49 0.00 15.99
9.52 0.43 0.04 98.04
10:26:41 AM dev104-2 21436.79 342596.23 0.00 15.98
9.17 0.43 0.04 94.34
10:26:42 AM dev104-2 22525.49 359749.02 39.22 15.97
10.18 0.45 0.04 98.04

now to demonstrate "write stalls" on the problemtic box:
10:30:49 AM dev104-3 0.00 0.00 0.00 0.00
0.38 0.00 0.00 35.85
10:30:50 AM dev104-3 3.03 8.08 258.59 88.00
2.43 635.00 333.33 101.01
10:30:51 AM dev104-3 4.00 0.00 128.00 32.00
0.67 391.75 92.75 37.10
10:30:52 AM dev104-3 10.89 0.00 95.05 8.73
1.45 133.55 12.27 13.37
10:30:53 AM dev104-3 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00
10:30:54 AM dev104-3 155.00 0.00 1488.00 9.60
10.88 70.23 2.92 45.20
10:30:55 AM dev104-3 10.00 0.00 536.00 53.60
1.66 100.20 45.80 45.80
10:30:56 AM dev104-3 46.53 0.00 411.88 8.85
3.01 78.51 4.30 20.00
10:30:57 AM dev104-3 11.00 0.00 96.00 8.73
0.79 72.91 27.00 29.70
10:30:58 AM dev104-3 12.00 0.00 96.00 8.00
0.79 65.42 11.17 13.40
10:30:59 AM dev104-3 7.84 7.84 62.75 9.00
0.67 85.38 32.00 25.10
10:31:00 AM dev104-3 8.00 0.00 224.00 28.00
0.82 102.00 47.12 37.70
10:31:01 AM dev104-3 20.00 0.00 184.00 9.20
0.24 11.80 1.10 2.20
10:31:02 AM dev104-3 4.95 0.00 39.60 8.00
0.23 46.00 13.00 6.44
10:31:03 AM dev104-3 0.00 0.00 0.00 0.00
0.00 0.00 0.00 0.00

that was from a simple dd, not random writes. (since it is in
production, I can't really do the random write test as easily)

theoretically, a nice rotation of disks would remove that problem.
annoying, but it is the price you need to pay

--
Jeff Trout <jeff(at)jefftrout(dot)com>
http://www.stuarthamm.net/
http://www.dellsmartexitin.com/