MaxCPU

[Paul Peeler]

Can anyone advise me on what the MaxCPU value should be based on in the Spotcloud Quota? Meaning, my Max VMs number is based on memory. Should Max CPUs be based on Max VMs in some way?

[SE Subs]

MaxCPU (I've always presumed) is the maximum number of physical CPUs (or cores) that can be allocated to your VMs. Then you work out your over subscription ratio of VMs to cores. I could be completely wrong though ...

[Derek Anderson]

This number should be less than, or equal to the number of CPUs in your server with the least CPUs. ie: if you have a server with only 4 cores, this number should be 4.

It is actually good to keep this number at half of the minimum CPUs if possible, as it improves IO scheduling. If you have all 8 core or better hosts, then a max CPU of 4 will give better IO performance on average to the VMs.

[Derek Anderson]

I apologize; I was looking at this quota ticket while I was separately thinking about hardware templates. SE Subs is right. The MAX CPU in the quota is the maximum number of CPUs _total_ that a customer (in this case, spotcloud) can provision across all of their VMs. A good way to set this number is to target the number of CPUS that will be required if they use all the VMs allowed in the same quota, multiplied by your average hardware template.

ie: If your max VMs is 12, and the average hardware template has 2 cpus, then a good round number would be to have 24 cpus in that quota. This is only a rough guideline of course, and you can modify it to meet your needs/expectations.

As for the hardware template, that is where my statement about CPUs applies. Don't hand out 16 core hardware templates if you only have 16 core hosts, or you may end up blocking on IO in the host while a VM pins all the CPUs.