Number of vCPU and load on a ESXi Host question?

[sandow]

We have 10 ESXi 6 host with 2 CPU's that have 8 Cores each with Hyper Threading.  I understand this gives me the ability for a maximum of 32 cores on a virtual client.  I have a situation where a vendor wants a Database server and is requesting that we have 32 cores in the virtual environment.  I am in the 30 to 50% CPU range across host.  I have a little concern about maxing out a VM client with 32 cores like that.  So my question is would this be recommended to do and would I see any major performance hit if we did do this?  Also what would kind of happen on that Host that this client would reside on?  Would it dynamically move other clients off and basically this single client would be on one host?  I am also considering as part of this project adding 2 additional host to the environment. Thanks for any responses.

[battybishop]

From my understanding you should not consider the Hyper Threaded core as a full second core so be wary if the supplier is requiring 32 cores on the virtual client. Also consider that ESXi requires processing requirements as well, I would normally allow 2 cores to ensure ESXi functions properly.

[Mattallford]

‌I'm always skeptical when I see requests come through like this, especially from vendors.

As mentioned, you really want to look at the physical cores in your system when doing performance based analysis.

I'd very pushing very hard to start a lot lower than their request. I usually treat these as a 'let's compromise and I'll give you X amount of vCPU and then show me with performance monitoring metrics that you require more'. I'd sometimes also request that the vendor give us a reference for other customers that are running the application, hopefully at a similar scale, to see what they observed.

If you did give them 16vCPUs and have DRS enabled on the cluster, DRS will attempt to move machines around in the cluster to ensure the VM is getting the resource it requires. If you proceed with the request, you'll want to monitor it very closely and make sure you don't run into any issues with ready time etc.

Cheers, Matt.