I am monitoring my Storage Array's performance and I was wondering what Cache Write Pending (CWP) Levels are recommended/normal for my system?
- Virtual Storage Platform (VSP)
- VSP G/F Series Arrays (G1X00, F1X00, GX00, FX00, G5X00)
- HUS VM
Hitachi recommends that CWP remain below 40% for open-systems and 30% for mainframe systems. Levels above these values will start to see elongation in response times and if CWP hits 70% then inflow control will trigger which will, by design, impose a slow down on host IO inbound to the CLPR that hit 70%. This is done so that the array can emergency destage data from cache to disk.