Well, a snapshot consolidation on this disk is not possible because the base virtual disk is not only provisioned with a size that exceeds the datastore size, but is also a thin provisioned virtual disk. Currently the base disk consumes ~178GB, and the snapshot ~117GB, so that there's no free disk space available on datastore1, that's needed for the snapshot consolidation.
What can you tell me about "/vmfs/volumes/USB"? It's listed as a VMFS datastore, but VMware doesn't support datastores on USB devices!? Is it just the name that's confusing? In case that this is a supported datastore, it could be used to clone the VM, and consolidate its snapshots.
André
PS: Ups, schon wieder in Englisch. Ich werde alt