Is the performance of a RAM drive inside a VM comparable to native hardware?

If I define a ram drive inside a VM will it behave the same as a ram drive on bare metal (with in reason). I am looking to setup a VM on my KVM node that will run a few games. Yes, one of them is Minecraft... which what I would use the ram drive for.

From the way I see it RAM is RAM but since the hypervisor is in between the VM and baremetal. I imagine it plays some part in the process and may have an impact on the overall performance of the RAM drive.

Is this the case or am I incorrect in my assumptions?

ianc1215

Posted 2016-02-24T03:02:17.377

Reputation: 2 884

Answers

The impact of hypervisor overhead should be minimal - typically its less then 5% for a VM.

Although the host does intercept and remap memory, this function is now largely done in hardware so its quite efficient. Have a look here, or the section "memory management" here for a simpler read.

davidgo

Posted 2016-02-24T03:02:17.377

Reputation: 49 152

So I would allocate a ram drive the same way I would on bare metal? No special tricks required? – ianc1215 – 2016-02-24T04:25:51.053

Correct. (No special tricks that you need to do - thats all done by the Virtualisation system). Most serious computing run heavily on VM's (abstraction allows control and increases resistance to failure), so its entirely reasonable to do.. – davidgo – 2016-02-24T04:27:48.133

In actual testing,

the VMWare ESXi 6.0 hostest Windows 8.1 guest operates at 300-1100MB/s
- using a 100% reserved memory
bare metal that's less powerful usually operates at 1000-3300MB/s

using SQLIO testing at a variety of block sizes and outstanding IO counts, while using an imDisk ramdisk.

Anti-weakpasswords

Posted 2016-02-24T03:02:17.377

Reputation: 481

Your result is very interesting, although I wonder if there are other differences at play here due to different hardware ?. According to http://sqlblog.com/blogs/linchi_shea/archive/2009/07/29/performance-impact-memory-effectiveness-of-virtualization.aspx, performance was about 83% of native in 2007 - before hardware optimizations had taken hold.

– davidgo – 2016-02-24T19:24:28.693