I wanted to create both an external backup as well as a 2nd ready-to-run VM on the 2nd datastore.
I removed all the snapshots, shutdown the VM and exported the OVF file to a computer, adjusted the size of the original VM, booted into Gparted to update the partition and reboot. All okay.
I then tried to deploy the OVF to the alternate datastore (235GB thin, 250 thick according to the deployment wizard). I've tried both thick and thin but receive the error "Failed to deploy the OVF. The operation was cancelled by the user".
I then manually uploaded the VMDK & OVF file to the 2nd datastore and tried to inflate but then received the message "A specified parameter was not correct. The disk is not thin provisioned.".
Based on (http://pubs.vmware.com/Release_Notes/en/vsphere/55/vsphere-vcenter-server-55u3-release-notes.html) I suspect there is something similar in 5.1. However I have no idea what to do now...and I'm concerned because it appears that my backup plan may not work if there was a critical problem.