Well the thing is that the copy job is kept running on the server, even if you close the vsphere client, but given it is a full copy, yes it can take a lot of time for 2TB
Given the ssh is not closing the connection, but the vmkfstools, I would discard any network/timeout issues at the ssh layer.... I had never suffered that problem.
Have you tried using a different datastore just to rule out a problem on it ?