vsphere HA and calculated failover capacity

[Sedoadmin]

Hello,

after reading several articles about the failover capacity for vsphere HA I still do not understand the following situation.

• Cluster configuration: two identical servers with 256GB RAM each.
• vsphere HA is turned on with response "restart VMs"
• Admission control configuration:
  • 

Cluster summary says:

Current resource consumption

vsphere Availability:

If I got that right, a tolerated number of failed hosts=1 in a cluster with two hosts should yield "Memory and CPU reserved for failover" of 50%, not 100%.

At the moment I cannot start further VMs due to the following error message: "Insufficient resources to satisfy configured failover level for HA".

I am wondering why is that? The cluster's memory is used less than 50%, with another VM using 4GB it would still be less than 50%. So why does vsphere complain about the failover level and shows 100% reserved memory and CPU for failover?

Thanks for your help

[TheBobkin]

Hello Sedoadmin

Likely because you have this set:

Bob

[Sedoadmin]

Why do I have to overwrite the calculated values? I could overwrite the calculated values for failover capacity. However, why does vsphere not calculate 50% of reserved capacity by itself? Two cluster hosts (equal amount of RAM) with one tolerated failure would be highly available if 50% of memory are reserved (IMHO...)

[TheBobkin · Accepted solution]

Hello Sedoadmin

This appeared to be set to 100% as default when I did not have it enabled and then when I enabled HA it changed the default values based on calculations of the resources in the cluster to a sensible value (e.g. 35% CPU in a 3-node cluster) - try unsetting/setting it again and see if this calculates correctly (and of course other basics such as both hosts being out of Maintenance Mode and able to configure HA successfully).

Alternatively test does changing this to 50% CPU, 50% Memory allows you to power on VMs.

Are you intending on running one host as standby with no VMs or just reserved ~50% on both hosts? If the former then likely better off configuring 'dedicated failover hosts' instead of 'Cluster Resource Percentage'.

Bob

[Sedoadmin]

Thanks for your hint: setting the override option and unsetting it again worked! Now vsphere calculated 50% reserved resources for failover as expected. The warning in the cluster regarding the failover resources disappeared.