SATA on mptsas performance

[Mirko Benz <mirko.benz@web.de>]

Hello,

We are testing the following setup:
- LSI SAS3442X controller
- Promise J300S SAS JBOD connected via the external port of the SAS 
controller
- 10 SATA disks (Seagate) in the JBOD
- Linux kernel 2.6.16RC2 on a INTEL Dual Xeon Server, 2.8 Ghz, 64 bit mode

LSI SAS driver provided by the kernel finds the JBOD and the disks.
Single disk performance is like attaching via a SATA controller from the 
chipset.
Testing with multiple parallel drive accesses gives very poor results 
and high system utilisation.
Tests performed with parallel invocations of dd with bs=32k. Values in MB/s.

# of disks    READ    AVG    WRITE        AVG
1    60    60,0    58    58,0
5    310    62,0    288    57,6
6    344    57,3    336    56,0
7    259    37,0    375    53,6
8    226    28,3    391    48,9
9    245    27,2    402    44,7
10    265    26,5    405    40,5

Up to 5 drives it looks as it should. Then the performance goes 
significantly down for READ operations.
The card is plugged in a 100 MHz PCI-X slot. No other activity on the 
system.

Any hint?

Thanks,
Mirko