High availability multi-controller configuration - Cyclic CM

ETERNUS disk storage systems can operate with up to eight controllers (*Note). The ability to operate a multi-controller configuration enables disk storage system performance to be maintained as high as possible even if one of the controllers fails. This ETERNUS disk storage system feature is called the Cyclic CM function.

For example, if one controller fails in a four-controller configuration, the remaining three controllers guarantee 3/4 of the maximum possible performance until failure repair, while 2/3 of the maximum performance is guaranteed in a three-controller configuration. With the Cyclic CM function, write data is also duplicated to cache memory on different controllers. If one controller fails, reconfiguration of cache memory is possible using the data in the redundant controller's cache memory. This method fully maintains controller redundancy even after a controller failure.

The figure below shows a three-controller configuration.
Four or eight-controller configurations operate in the same way.