Hi MoldRiteBud and welcome to the community!
Firstly I'm assuming you are talking about Storage vMotion
Secondly - you should have little fear of moving a VM with 3.5TB of VMDK assuming your infrastructure is sound. There have been a number of changes to the way Storage vMotion works with probably the biggest change being the implementation of the mirror driver. This makes moving a VM much more reliable and reduces the time to migrate: vSphere 5.0: Storage vMotion and the Mirror Driver - Yellow Bricks
Also if the VM consists of multiple disks then you could just move the database drives a VMDK at a time if really worried. I think this actually adds more risk but could be an option.
As with any change in our industry make sure you have a tested recovery plan.
Kind regards.