MSA500 multipath diskpart problems under winpe

[MarcelR]

We use an installation setup, which relies on diskpart under WinPE 2.0. This runs fine with a single connected msa500.
With a MSA500 with redundancy kit (Each of the two servers has TWO 642 controller boards) diskpart will take hours to start. If I disconnect one of the two scsi cables, diskpart runs fine again. This behaviour is only seen if the disks on the MSA500 contain already some partitions. It looks like diskpart has troubles with the fact that it's seeing the partitions twice. I tried to install Multipath software in the WinPE installation, but I think these drivers don't work under WinPE because the problem still exist.
How could I resolve this problem? Disconnecting the second cable is not really a nice solution...