Copying files from Datastore to local server very slow

We have ESXi 4.0.0 (208167). Using a vSphere Client, copying VMs from the datastore to a local Server is taking ages! A 300GB image takes approximately 9 hours and we have 4 VMs to move. We have a gigabit network and the harddisk are all SAS in a RAID10. Any idea if this is usual or what the problem could be and how we could increase performance?

Thanks