Created attachment 160351 [details]
syslog

I have an SAS controller with LSI SAS 2008 controller in a PCIe slot with only four lanes where the card can use up to eight lanes. I have the following issue. Lets assume there are four drives attached to the controller (sda...sdd). I use the following simple benchmark "cat /dev/sdX | pipebench > /dev/null". When accessing every drive individually, every thing works fine. However when I run the experiment on sda and sdb concurrently, it still works on sda but the benchmarks stalls on sdb. When I kill the benchmark after some seconds I see the error messages in the attachment. 

However, it gets more strange. When I run the benchmark concurrently on sda and sdc every thing works as expected. When trying to read sdb or sdd concurrently it always results in the error described above.

I also tried to change the hardware setup and only used every second connection of the card. However the result stayed the same: concurrent access to every second disk fails.

In the same machine I have the same SAS controller model in a PCIe x16 slot and there every thing works like a charm. I also swaped the cards and the issue stays with the PCIe x4 slot. So a defective card as the source of the problem can be ruled out.

Thank you