Hi everyone
Today I attempted to place a host into maintenance mode and received the infamous "Insufficient resources to satisfy configured failover level for vSphere HA". I worked around this by temporarily disabling Admission Control but this got me wondering how the cluster would tolerate the loss of one of the hosts.
This is what my cluster looks like:
- 2 x Dell PowerEdge R720s with 96GB memory and 2 x Intel Xeon E5-2650 CPUs (12 cores) per host
- ESXi 5.0 Update 1 + latest patches
- vSphere HA enabled
- Admission Control Enabled (set to reserve 50% of resources)
- DRS enabled
- 16 Windows VMs with CPU configurations ranging from 1 to 4 vCPUs and 1GB to 4GB Memory.
I have researched the problem in an attempt to ascertain what is causing the problem. To this end I put together an Excel-based calculator to determine the cluster failover capacity. The calculations are based page 22 of "vSphere Availability - ESXi 5.0".
My posting has two parts to it:
1) The attached calculator which I would be very grateful if someone would review and confirm that it is correct (hopefully it is and others will find it useful). I have protected the sheets "CPU" and "Memory" so they can be used as examples. Simply edit the host CPU/Memory details in the other sheets to match your environment. I left my cluster's details in their as I thought people could use it as an example. If you like I can clean this up.
2) A question: how will my cluster behave with the loss of one host? If the behaviour of placing one of the hosts into maintanance mode is anything to go by not all the VMs will start on the surviving hosts as the CPU requirements cannot be met. However, I have read that in a failover event HA will ignore the Admission Control Policy and attempt to start the VMs on the surviving host. Can someone please confirm this?
I hope this is clear enough. If not, I'll be happy to provide any additional information.
Thanks very much!
Sean