The statit output below is from a 12 disk SATA aggregate on a FAS960. The load is from a jetstress test that I let run only for a few minutes.

Disk Statistics (per second) ut% is the percent of time the disk was busy. xfers is the number of data-transfer commands issued per second. xfers = ureads + writes + cpreads + greads + gwrites chain is the average number of 4K blocks per command. usecs is the average disk round-trip time per 4K block.

disk ut% xfers ureads--chain-usecs writes--chain-usecs cpreads-chain-usecs greads--chain-usecs gwrites-chain-usecs/aggsa/plex0/rg0: 3b.16 43 19.48 0.33 1.00 30786 17.86 30.41 1082 1.29 9.46 560 0.00 .... . 0.00 .... . 3b.17 43 19.43 0.33 1.00 36786 17.86 30.41 1099 1.24 8.60 485 0.00 .... . 0.00 .... . 2b.18 40 18.72 0.67 1.00 16893 17.43 30.88 1027 0.62 14.50 554 0.00 .... . 0.00 .... . 3b.19 40 18.00 0.00 .... . 17.17 31.33 1050 0.83 10.66 566 0.00 .... . 0.00 .... . 2b.20 40 17.69 0.00 .... . 17.07 31.47 1037 0.62 16.27 506 0.00 .... . 0.00 .... . 2b.21 42 17.67 0.00 .... . 17.10 31.46 1097 0.57 13.54 412 0.00 .... . 0.00 .... . 2b.22 41 17.76 0.02 1.00 16000 17.07 31.47 1115 0.67 13.11 474 0.00 .... . 0.00 .... . 3b.23 40 17.91 0.00 .... . 17.14 31.32 1045 0.76 13.53 545 0.00 .... . 0.00 .... . 2b.24 42 18.19 0.00 .... . 17.29 31.11 1160 0.91 8.76 1078 0.00 .... . 0.00 .... . 3b.25 41 17.95 0.02 1.00 9000 17.19 31.29 1077 0.74 9.77 614 0.00 .... . 0.00 .... . 2b.26 43 17.88 0.00 .... . 17.12 31.42 1167 0.76 12.72 747 0.00 .... . 0.00 .... . 3b.27 41 18.17 0.00 .... . 17.19 31.25 1103 0.98 11.29 585 0.00 .... . 0.00 .... .

My question is, how do you interpret this data correctly? For example, was 43% of 3b.16¹s time busy issuing 17.86(ignoring reads and cpreads) write commands that wrote 30.41 4KB blocks (120KB¹s) and took 1082(somethings?) to return.

Is an xfer the same thing as an I/O?

What is the measurement for usecs?

Thanks for the help.

- Carl

On 3/15/06 11:24 AM, "Blake Golliher" thelastman@gmail.com wrote:

I ususally gauge that I can get 40 to 50 iops / sec under a 10ms responce time. So a little less then half of what a 10k RPM (fcal) disk can do.

-Blake

On 3/15/06, Carl Howell chowell@uwf.edu wrote:

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Does anyone have any SATA performance data? I know that there are many variables when measuring disk i/o, so any information would be appreciated.

Thanks,

-Carl