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Performance Policies - Caching Question

 
jkoelker
Occasional Contributor

Performance Policies - Caching Question

Hello, I've got a question in regards to performance policies on my CS1000 device. I don't have a lot of SSD storage on my device and currently only have one volume pinned to the SSD drives. When I set this device up, I created my own performance policies based off of the Vmware ESX 5 policy which states 4KB, Compression enabled and Caching enabled. But instead of Caching enabled, I chose not to Cache for my policy. Most of my basic virtual machine servers are tied to this policy with caching disabled. Can someone explain that part of the performance policy to me? Does that directly cache to the SSD's or is that another part of the Nimble that caching is occuring for that part? 

I want to be sure I'm not missing out on performance for something I've misunderstood. I can certainly change the performance policy for my volumes to the policy with caching enabled if I'm not adversely affecting anything else. 

Thanks in advance for the help.

1 REPLY 1

Re: Performance Policies - Caching Question

The defaut caching policy of ESX5 on HFA are with both Cache & Compression enabled.

 

With Cache enabled means array will use default caching algorithm to catch the "Cache worthy" data to SSD during data write path,  which are random I/Os.    All data (including random plus sequential I/O) will stored in spindle media with Triple Plus Parity protection.  With this approcah data in read cache will be very dynamic based on write pattern; without requires Cache warm up based on user access pattern to exsiting data written into array.

 

If you disable the Caching in performance policy, those LUN based on that policy will skip data caching during write, and SSD will need to be re-warm up by client access or prefetch from array.

 

To learn more about CASL:

https://www.youtube.com/watch?v=ZjSfVKncEKM

 

 

 

 

Thomas Lam
Field CTO - HPE Nimble Storage