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Hitachi Vantara Knowledge

What Is The Cause Of High Cache Write Pending

 

Question

I see high levels of Cache Write Pending on my array, what could be causing this?

Environment

  • Virtual Storage Platform
  • VSP G/F Series Arrays (G1X00, GX00, G5X00, F1X00, FX00)
  • HUS VM

Answer

While there are certainly a number of potential factors for high Cache Write Pending, the number one cause of this is the over utilization of disk/parity groups. When disks are overworked, the array can no longer flush data from cache fast enough to keep up with inbound IO.  Which this occurs, data will begin to back up into cache which elevates the cache write pending levels.  Hitachi generally recommends that spinning disks remain under 50% utilization and solid state disks remain under 100%, this will help to insure that data can flush from cache at an acceptable rate to keep up with normal workloads.

Additional Notes