Thanks for the reply.
I'm still not sure about the process. Does it copy a "snapshot-in-time" version? In other words, if I run xe vdi-export
am getting a copy of whatever was there, at that moment?
I understand that there are serious problems in trying to copy anything that is "live". For example, FSArchiver can be forced to copy a live system and while it does this safely, there may be inconsistencies in the data.