[CentOS] Performance Issues

Sun Sep 2 15:11:45 UTC 2007
Dan Dansereau <ddansereau at hydropoint.com>

My apology for cross posting

We have a DELL6850 with 8Gbytes of memory,  four 3.2Ghz CPU's , perc 4
raid controller, with fourteen 300Gbyte 10Krpm disk on a powervault
220s, And a powervault 124T  LTO-3 tape systems on a separate
160Mbyte/sec adaptec SCSI card.
The disks are configured as two 2Tbyte raid 0 partitions using the perc
4 hardware. 

The problem is - reading from the disk, and writing to the tape is
pathetically slow.
The specs say I should get around 80Mbyte/second - in reality - is about
500 Kbytes/second 

Writing just to tape, using /dev/zero as input and dd to write, I can
get up to 60Mybte/second, indicating that the tape drive and scsi card
is functional from a hardware perspective. Since I can read and write
data to the disks - I assume that they are functional.
The files are 80Mybtes for the minimum size that I am writing to tape. 

DELL Support hides behind the fact that CENTOS is not a supported OS,
But RED HAT is - so switch to it, so DELL can get RED HAT Support
involved. And the fact that Rocks is a modification to an unsupported

I have tried using various block size in tar from 256 to 8192 - with
minimal success.

Does anybody have any experience on setting the OS/Kernel parameters to
utilize the hardware at something more then a snails pace?
Suggestions on what I could test and/or try?
Is there a standard disk / tape IO test package that could test the
speed/performance of the disks and /or tapes?

Thanks for your help
Dan A. Dansereau