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E-Series: Write back caching forcibly disabled alert

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Applies to

E-Series storage array

Description

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

Important Notes

  • 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. 

 

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