What refresh process is appropriate in this case?

A customer is upgrading their EMC Isilon nodes as part of a technology refresh. The nodes to be replaced cannot be upgraded to the later version of OneFS that is required by the newer nodes.

What refresh process is appropriate in this case?
A . Use SyncIQ to migrate the data from the old cluster to the new cluster
B . Add the new nodes to the existing cluster and use SmartPools to migrate the data
C . Add the new nodes one at a time and SmartFail out the old nodes
D . Downgrade the new nodes to the version of OneFS running on the old nodes

Answer: A