You must add the aggr to a resource pool and attach it to the node of the dataset to which the volume you plan to migrate belongs too.
For example if you have a dataset with backup policy you must attach the aggr to a RP and attach it to the backup node of the dataset.
Secondary Space Management, which migrates individual volume, which are part of dataset.
The rule or conditions that needs to be met for a volume to be migrate capable is the following.
SSM doesn't migrate the following.
Root Volume of a filer or vfiler is not migration capable.
Volumes with client facing protocols like CIFS, NFS, iSCSI,FCP.
Volume which are parents of flexclones.
Volume which have unmanaged relationships.
If there are client facing protocols.You must remove the client facing protocols you will be able to migrate using SSM, but during the entire duration of initial baseline from old destination to new destination.
After the inital baseline SSM will modify the relationship, you dont have to rebaseline the downstream relationship and also wont loose any already registered backup.