To migrate an external volume greater than 4TiB, first create a data direct mapping (DDM) pool.
DDM pools are flagged DDM Enabled: YES in the Pools window and in the pool details windows.
To add a DDM pool, navigate to the Advanced tab of the Create Pool window and select Yes under ENABLE DDM?.
For DDM pool sizing, see the "Estimation of the required capacity of pool-VOLs with system area in a pool with data direct mapping enabled" section in the storage system Provisioning Guide.