are two VMs in totally fair condition to run database performance comparison?

[Seanfff]

Hi,
We are running performance comparisons of databases on two VMs on one physical machine. We need to create totally fair condition in these two VMs to compare the two databases. We are not that familiar with VM, so we got 2 questions:

1. Say, if we create two VMs with the same configuration, (2 physical cores, 16G memory, 100G SSD), on a physical machine (8core, 64G memory, 250G SSD), is it physical isolation of the resource(CPU, memory, SSD) in two VMs? The CPU, memory, SSD assigned to one VM, will not be used by the other VM, nor by the host system in any case? is this right?

2. Will the two VMs compete for the resource on the host system? for example, memory...When the two VMs load very big files from SSD at the same time, will they compete for the memory file cache on the host system?

Thanks,

[socratis]

Think of your VMs as two applications. With separate data files. They each have their own requirements for CPU, RAM, HD. They share some resources, like system DLLs, but for all terms and purposes they have their own unique requirements.

So, in short:
1) each one and their host has their own needs. Make sure that their sum does not exceed what you have available. Same as if you have two large-requirements applications.

2) The virtual HD is a (usually huge) file of several GB. I highly doubt that the host OS will cache the file. But, if you read several GB and several different GB, your host might have issues servicing two large requests at the same time. Same as if you have two large-requirements applications.

[Seanfff]

Thank you, Socratis.