esxi 5.5+ host cache best practices?

[PeterMu]

I migrated from a HP EVA array to a Nimble CS300 a few months ago, at start I had host caching configured for our esxi hosts as they had mirrored SSDs installed in them. My thinking is local SAS storage will be faster than navigating an HBA to get to the Nimble - am I right in that? Has anyone played with host caching and Nimble - seeing what effect turning it on an off has on performance and utilization on the array?

[tmoore106]

Swap caching or Virtual Flash (which became available in 5.5)??

[PeterMu]

Ah I meant swap caching originally. I would be curious though if anyone has tested with vFlash though if there is a performance advantage

[tomatthe119]

I'd be curious to see some input on this as well.  What type of performance boost were you looking for?  The latency to the array is already so low I can't see the local ssds doing much.

[pflammer23 · Accepted solution]

Hello Peter,

Not sure how much vFlash improved with vSphere 6, but with 5.5 the function is limited.

It is not a dynamic resource. You can’t just put 2 TB SSDs in the server and say use them for read cache.

You have to dedicate some space to each VM which makes it rather... well not complex... but time consuming.

Also what happens if you move that VM to a different server and on that servers is not enough vFlash capacity left for this VM?

I also have to agree with Travis!

A good designed network (10GBit) should add well below 20 microseconds of latency.

I don't think there will be a notable difference whether the IO comes from local SSD or a Nimble SSD.

Pierre