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@jefftrout.com>
http://www.stuarthamm.net/
http://www.dellsmartexitin.com/