Do you have a different raid card you can try beng? or I would be interested to know if they work ok using the onboard SAS controller and open-e soft raid. If it doesnt work with the onboard your issue maybe the enclosure.
Yep, that is our next plan, but also have problems with the GBE Nics on this machines as well (1% sustained throughput....) yet the hdparm output is 350MB/s, plus it is also "sort of in use.. by the client" so they don't want us to touch it unless we are sure of a fix.
I'd rather not use the onboard, as one of the reasons for this config was to include the separate cards for DRP, ie technically we could switch the card/drives to another box and bring the array back up.....