topic Re: Understanding cache churn in Infosight in Array Performance and Data Protection

Understanding cache churn in Infosight

I McWilliams — Tue, 31 Mar 2015 10:39:09 GMT

I was hoping someone could explain the cache churn graph on Infosight to me.

For example if the graph shows Volume-A with a Business Hours, small I/O value of 25% does this mean...

25% of data removed from cache came from Volume-A
25% of data added to cache was from Volume-A
25% of cache space is currently allocated to Volume-A
25% of cache hits were from data on Volume-A

I would assume it was one of the first two (churn implies change) but it would be good to get some confirmation of this and how to better understand the information presented.

Thanks

Iain

Re: Understanding cache churn in Infosight

Valdereth — Tue, 31 Mar 2015 12:44:15 GMT

It would be good to get some clarification on this, I agree, churn gave me the same impression of change as well.

If you hit "More..." above the graphs you'll get more information about the tab. My my understanding is that its showing what percentage of cache hits are coming from which volumes. So you should be able to use this in conjunction with the cache utilization to hone in on volumes that are utilizing cache that may not require the latency benefit of reads being served from SSD. I've only really used this tab when looking at an array that's near 100% cache utilization.

Re: Understanding cache churn in Infosight

I McWilliams — Wed, 01 Apr 2015 08:22:40 GMT

Thanks, I suspect you may be correct. It's not what I would expect from a section described as "churn" but the word may have a different meaning in the US compared to the UK.

It's not an issue, I'm just trying to better understand this new Nimble array.

Re: Understanding cache churn in Infosight

tmoore106 — Wed, 01 Apr 2015 14:31:01 GMT

These charts show cache churn (usage) by time of day, I/O size, and Volume Name

I agree the use of the "churn" word can be confusing, but it it means usage in the context of the charts on that tab. So in your scenario, 25% of cache space is currently allocated (being used) to/by Volume-A.

HTH

Re: Understanding cache churn in Infosight

I McWilliams — Wed, 01 Apr 2015 14:39:43 GMT

Thanks Todd