the cache hit ratio is not well prepared for the alerting as I can see. I'll point this out in a team.
In the meanwhile you definitely can use "Custom SWQL Alert (Advanced)" and define your custom "where" condition as following:
WHERE StorageArrays.Statistics.ObservationTimeStamp = StorageArrays.LastSync AND StorageArrays.Statistics.CacheHitRatio < 10
Translation for this condition is that: "I'd like to have an alert for storage arrays where their total cache hit ratio is less than 10%". Modify that condition as you wish and if you want to have specifically cache hit for read and write, use following in the condition:
Cache hit Ratio Total: StorageArrays.Statistics.CacheHitRatio
Cache hit Ratio Read: StorageArrays.Statistics.RatioRead
Cache hit Ratio Write: StorageArrays.Statistics.RatioWrite
You can use the cache hits for Storage Arrays, Pools, Luns, NAS Volumes, File Shares, but do not forget adapt it into the "where" clause.
Perfect! Thanks for your help.