Why is it that in order to relocate some of my VM's does the UI say that the machine needs to be powered off in order to complete?
More than likely it might have to do with the differences in the ESX hosts like CPU incomatability -
Shouldn't be that. All of my hosts are identical.
in order to change both host and datastore at the same time, the VM must be powered off. However, if you just want to change host, use vMotion, if you just want to change datastore, use Storage vMotion, if you want to change both, while online, first vMotion, then Storage vMotion.
And actually as I know think about it I am wrong since in Storage vMotion the VM does not change hosts -
storage vmotion does not require down time. the only reason is that you're moving to a storage that is current not present in the local host. could be local storage of another host.
check to see if your vm's have snapshots that need to be committed...