If removing a storage server results in the number of storage servers being used by the Oracle RAC cluster dropping to fewer than five, and the voting files reside in a high redundancy disk group, then you should add quorum disks to the database nodes, if they are not in place already. See Adding Quorum Disks to Database Domains.
Before removing the storage server, add the quorum disks so that five copies of the voting files are available immediately after removing the storage server.