This article describes the procedure to troubleshoot "Write-Back Caching Forcibly Disabled" on E-Series systems.
Write-back caching was disabled on one or more volumes. This problem can occur for the following reasons:
- Battery Failure
- Battery below minimum capacity
- The cache size memory of the controllers are different
- Cache Reconfiguration
- A Cache Data-Restore operation is in progress, which interrupted the normal write-back caching process
- The space in the cache backup device is insufficient for storing the cache
- Memory parity error
- Simplex configuration - cache cannot be mirrored
- When write-back caching is enabled when volumes are configured, write-back caching improves I/O performance. When write-back caching is disabled, the system goes into write through mode, meaning that the I/O will get acknowledged after it is written to disk rather than when it is written to cache. In such case, I/O performance to the volume or group of volumes can be seriously degraded depending on the drives.
- The error triggers a critical event.
- The controller is in the Notified state. When write-back caching is enabled, the system transitions from Notified to Optimal after all volumes configured to use write-back caching are restored.
- When the system transitions from Notified to Optimal, an information MEL event is logged to show that all normal write-back caching capabilities are restored for all volumes in the system.
- While in the Notified state, a forced-disable of write-caching on any additional volumes has no effect, and no state transition occurs.