Virtual Kim

@Kim_Bottu … Virtually Gung Ho

vMotion: debunking connectivity and performance myths

I have heard many assumptions over the last couple of years but one of them which really poked me in the eye is the following one: “When you vMotion a VM there is no impact on that VM’s connectivity or that VM’s performance.”

I will try to debunk both of them. So let me give you a simplistic graphical representation in the form of a video I made of what can happen when you vMotion a VM which is already running at a high CPU clock speed. You will see the impact of 2 vMotions on the same Test VM.

  • 1. The connectivity can be interrupted.
  • 2. The VM will be stunned for a period of time during which the dirty memory pages are transferred.
  • 3. There will be a negative impact on CPU performance for VM’s which are already running at a high CPU speed. 

The test VM runs 4 videos at the same time using VLC player. All players run locally playing a locally saved video. I did not test a scenario where a lot of data is being read or send remotely.

I have also performed the same test with 1 more instance of VLC player running (5 players instead of 4) and during vMotion, the ping command just stopped running for sometimes 5 , then 10 or up to 30 seconds. For applications which are really sensitive to high latencies, this is very bad news.

VM’s which I think should be prevented from performing a vMotion during office peak hours, unless there are no other VM’s to vMotion to free up resources on a host which is out of resources:

  • High performing Database VM’s
  • High performing Exchange VM’s
  • Basically all VMs which run applications which are highly sensitive to latency.

 

Advised reads:

Virtual machine performance degrades while a vMotion is being performed (2007595)

Video Playback Performance Degradation After Migration with VMotion (1001530)

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This entry was posted on September 3, 2015 by in Connectivity, Myth, Performance, vMotion and tagged , , , .
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