Did you configure it according to the MSCS Guide?
http://www.vmware.com/pdf/vi3_35/esx_3/r35u2/vi3_35_25_u2_mscs.pdf
Are you using the cluster across boxes scenario and physical or virtual compatibility mode RDMs?
Have you configured an additional, dedicated vSCSI controller in the VMs for those RDMs, set it to physical SCSI bus sharing, and set the RDMs to use identical SCSI IDs on this controller on both nodes?
Are you seeing the disks on both nodes when they run concurrently?
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