Cache Churn - infosight charts

[jayst136]

I'm really trying to understand the Cache Churn charts.

i'm looking at a chart which has been split by volume. The volume with the highest cache churn has 50% cache churn for small IO during business hours. The same volume has 71% cache churn for large IO during business hours. How should i interpret those charts?

The resource utilization chart confuses me a little as well, it shows 5% cache usage, but 5% of what actually? 

[chris24 · Accepted solution]

Firstly the volume with high large and small IO means that it is your busiest volume and responsible for most of the blocks in cache - it's probably a catch all data-store used by a host of machines, consider splitting up up the machines into separate volumes to give you a clearer idea of which volumes (VM's) are hitting your cache the hardest.

Cache utilization basically refers to "The amount of cache required/The amount of cache installed" - if you are at 5% it means you are using 5% of the total cache - i.e. you have a long way to go to utilizing your full 100% cache and have to consider buying more.

[jayst136]

thanks for the answer, makes it clear enough for me now!

[jayst136]

Looking again at the resource utilization chart, it has updated itself with new data and now shows 105% cache usage.
How should i interpret >100% cache usage ?

[jayst136]

ok the resources utilization chart now displays 72% for the cache, not at a new data point but at the same datapoint where 105% was displayed previously.

We'll see how it goes from here.