Indicates how this filter entry's row is stored - rows created through an external process may show readOnly or permanent, while ones created via SNMP typically default to nonVolatile. Admins check this to know whether a given entry can be modified or deleted via SNMP, since readOnly or permanent rows may not be editable that way. An admin trying to delete a stale filter entry that fails would check panaL2FiltStorageType first to see if it's marked permanent and therefore not removable via SNMP.