VM /ETC

How to increase the number of simultaneous VMotions of guests allowed between VMware ESX hosts has been covered many times already. In fact, check out the following blog posts on this topic for extra information and insight not provided here.

• Increase Simultaneous VMotions as well as Increase Performance
• Guest blog entry: VMotion performance » broche.net – VMware …
• VMware Communities: ESX Tips: Increase number of VMotions per host
• Increase number of VMotions per host

One possible scenario for changing this setting would be to temporarily increase VMotions allowed in order to evacuate ESX hosts within a short maintenance window. I prefer to leave the setting at the default, so for this scenario be sure to change it back after the maintenance is complete. if you read the links provided above, others suggest they have changed the settings permanently.

This rest of this post contains a cut and paste of the steps necessary to make the configuration change with a brief explanation about setting the appropriate value. I am pasting from a VMware Partner PDF communication assembled by Michael White, VMware engineer.

“How can I increase the number of simultaneous VMotion activities?

It is possible to increase the number of simultaneous VMotions but it is something that you should be careful of. Do not due it lightly or on a regular basis but in fact use it on a project basis when required.

While it is not documented by VMware officially, it is in fact supported. Really. You only need to change a variable in the vpxd.cfg file and restart VC. Use the steps below:

1. Connect to your vCenter server.
2. Locate the vapid.cfg file – it is normally in C:\Documents and Settings\All Users\Application Data\VMware\VMware Virtual Center.
3. Make a back up copy of vapid.cfg.
4. Edit the file and insert the information below between the and sections. X
5. The value of X is what you need to calculate carefully.
6. A cold migration has a cost of 1, and a Hot Migration (VMotion) has a cost of 4. So a value of 16 for X would mean you could do 4 simultaneous VMotions (4 * 4 = 16).
7. Now save your changes.
8. Restart the VMware VirtualCenter Server service to make the changes live.”

It may be obvious, but I’ll point out the above setting also means you could do 16 simultaneous cold migrations (VMs powered off): 16 * 1 = 16

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