I was re-reading the KB article on how to improve HA scaling. Apparently pre vCenter 2.5 U5 there was a problem when the amount of VMs that needs to fail-over exceeds 35. Keep in mind that it’s a soft limit, you can run more than 35 VMs on a single host in a HA cluster if you want to though.
To increase scalability up to 80VMs per host vCenter needs to be upgraded to 2.5 U5 and the following configuration changes are recommended:
- To increase the maximum vCPU limit to 192
- To increase the Service Console memory limit to 512 MB.
- To increase the memory resource reservation of the vim resource pool to 1024 MB.
- To include/edit the host agent memory configuration values. (hostdStopMemInMB=380 and hostdWarnMemInMB=300)
- 512
- 300MB
- 0 MB
- hostdStopMemInMB=380 and hostdWarnMemInMB=300
As you can see 1 and 4 are already the new default on vSphere. I would always recommend to set the Service Console memory to 800MB. With most hosts having 32GB or more the costs of assigning an extra 500MB to the Service Console is minimal. That leaves the recommendation to increase the memory reservation for the vim resource pool. I would recommend to leave it set to the default value. vSphere scales up to 100 VMs per host in a HA cluster and chances are that this will be increased when U1 hits the streets. (These values usually change with every release.)
What happens if you exceed 32 VMs per host or even 100 VMs in vSphere? Does it simply not start VM 33 or not restart any VMs at all? I need more VMs in my lab. 🙂
Its still a soft limit, vm# 33 will be started
Note that the VIM resource pool setting only applies, according to the article, to ESXi.
It will boot up, only VMware can’t guarantee it will be started when a failure occurs and HA wants to restart them