A controller board might fail due to unavailability of redundant cache memory because of an error in a controller board or cache memory. If this happens, system option mode 164 lets you change the type of operation to accommodate each user’s needs regarding writing of data from a host.
When SOM 164 is set to ON:
- The write-after operation is performed. When a host writes data while one of the controller boards is inactive due to a failure, the host is notified of the completion of data write when data is written to cache memory.
- The degradation of write performance of a single controller board in operation is reduced. However, if the active controller board also fails, the write pending data in that controller board is lost. If your system requires high data reliability like RAID, system-wide data redundancy measures are required.
When SOM 164 is set to OFF:
- The write-through operation is performed. When a host writes data while one of the controller boards is inactive due to a failure, the host is notified of the completion of data write when data is written to a drive.
- If the active controller board also fails, the write pending data in that controller board is not lost. However, write performance is compromised while only one of the controller boards is active. If you decide to set SOM 164 to OFF, you need to design a system that can tolerate degradation of performance such as I/O response.