Is there anyway to disable the parallel processing of disks while keeping the parallel processing of VMs.
No, in concepts of VB&R single task is equal to single virtual disk. Thus, parallel processing is defined by number of virtual disks (not VMs) that can be processed simultaneously.
I find that processing VMs with multiple virtual disks that are on the same datastore can really beat up the underlying physical disks.
But how this would be different from the situation when disks belonging to different VMs that reside on the same datastore will be processed at the same time?