Re: Performance problem - reads slower than writes

Stan Hoeppner
2012-02-01T07:29:33Z

On 1/31/2012 2:25 PM, Dave Chinner wrote:
> On Tue, Jan 31, 2012 at 02:16:04PM +0000, Brian Candler wrote:

>> Here we appear to be limited by real seeks. 225 seeks/sec is still very good
>
> That number indicates 225 IOs/s, not 225 seeks/s.

Yeah, the voice coil actuator and spindle rotation limits the peak
random seek rate of good 7.2k drive/controller combos to about 150/s.
15k drives do about 250-300 seeks/s max. Simple tool to test max random
seeks/sec for a device:

32bit binary: http://www.hardwarefreak.com/seekerb
source: http://www.hardwarefreak.com/seeker_baryluk.c

I'm not the author. The original seeker program is single threaded.
Baryluk did the thread hacking. Background info:
http://www.linuxinsight.com/how_fast_is_your_disk.html

Usage: ./seekerb device [threads]

Results for a single WD 7.2K drive, no NCQ, deadline elevator:

1 threads Results: 64 seeks/second, 15.416 ms random access time
16 threads Results: 97 seeks/second, 10.285 ms random access time
128 threads Results: 121 seeks/second, 8.208 ms random access time

Actual output:
$ seekerb /dev/sda 128
Seeker v3.0, 2009-06-17,
http://www.linuxinsight.com/how_fast_is_your_disk.html
Benchmarking /dev/sda [976773168 blocks, 500107862016 bytes, 465 GB,
476940 MB, 500 GiB, 500107 MiB]
[512 logical sector size, 512 physical sector size]
[128 threads]
Wait 30 seconds.............................
Results: 121 seeks/second, 8.208 ms random access time (52614775 <
offsets < 499769984475)

Targeting array devices (mdraid or hardware, or FC SAN LUN) with lots of
spindles, and/or SSDs should yield some interesting results.

--
Stan