Hello Dave,
"I was thinking it should just be a copy(raid 1) between the 2 nodes, so why not always mark if as "full data migration"?"
With default Storage Policy (PFTT=1,FTM=RAID1) it keeps a replica of the data on each data-node - it wouldn't be beneficial (nor compliant with the Storage Policy) to move a second copy of the data to the other node (only have to clone it all back later).
"That way you can shut it down as long as needed without having to worry about the Repair Delay Timer, etc?"
In the case of hosts in MM with EA, you don't have to worry about CLOM repair delay in a 1+1+1 or 2+1 or even a standard 3-node cluster as if it expires, where exactly would it rebuild the components to be compliant with the Storage Policy?
It wouldn't as it wouldn't increase FTT nor compliance and thus just delta resync should occur (e.g. the data it did not commit while out of the loop).
Bob