...
ERPS ring defined in command set protocols erps ring <ring-id> is a physical ring, however, ring instance can be thought as a logical ring on the physical ring defined in command set protocols erps ring <ring-id> instance <1 | 2>. A maximum of eight ERPS rings rings (including both major ring and sub-ring) are supported on a device, and a maximum of two instances can be configured for each ring.
...