When you set up vFiler units in an HA pair, both nodes must have MultiStore enabled to take over the partner. IPspaces created in one node in an HA pair must also be created in the partner system for failover to function correctly.
This means each storage system can host a different number of vFiler units, and the vFiler unit configurations on the storage systems can be different from each other.
These vFiler units include the vFiler units you have created and the default unit vfiler0. Therefore, for vFiler units on the failed storage system to work correctly after takeover, each network interface used by a vFiler unit in an HA pair must have a partner interface.