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[Condor-users] tuning a file server


some weeks ago, I had to move our file systems (/home and some data) to 
another server, equipped with 3ware 9000 cards, and using 8 400GB disks
in RAID5 with hot spare (2.3TB net capacity). To manage the disk space,
I had to switch to Linux kernel 2.6 - and there are indications that this
move caused some problems.
The file server has to serve 360 VMs in 180 dual-CPU machines, and if 
there are lots of small I/O operations, the iowait percentage goes up to
more than 80%! I have never seen that before (the previous server was
almost identical, kernel 2.4, 1.4TB each).
Now I suspect that the i/o strategies introduced with 2.6 kernels are 
badly configured... are there any suggestions?
The RAID is fast enough -

# hdparm -tT /dev/sda

 Timing cached reads:   2680 MB in  2.00 seconds = 1338.20 MB/sec
 Timing buffered disk reads:  358 MB in  3.00 seconds = 119.31 MB/sec

what I can see is of the order of 2MB/s read and write...

Close to the end of my wits,


Steffen Grunewald * MPI fuer Gravitationsphysik (Albert-Einstein-Institut)
SciencePark Golm, Am Mühlenberg 1, D-14476 Potsdam * http://www.aei.mpg.de
* e-mail: steffen.grunewald(*)aei.mpg.de * +49-331-567-{fon:7233,fax:7298}
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