ESXi Understanding Host Memory vs Guest Memory

As far as I know, there is no way to directly access a virtual machine console from the ESXi virtual server host.

Assuming that you have access to the VMware host server, you can use the VMware vSphere Client (from Windows) to access the system console. Click on the appropriate host, then on the Console tab. Click inside the console window to start typing at the console, and press Ctrl-Alt to escape the console window back to the local Windows machine.

After some (long) conversations with VMware support, I have come to the following understanding:

The number in "Reserved Capacity" is not a function of the memory configuration for the cluster's VMs. It is the sum of several factors: any memory reservations declared on VMs, a value calculated from the HA admission policy, and an additional amount for memory management overhead. The HA admission control value is directly derived from the admission control policy; in my case, since I had it set to tolerate a single host's failure, the total amount of RAM on one of my hosts was added to the cluster's reserved capacity.

Among other constraints, it appears that HA admission control will not allow the reserved capacity to exceed the RAM in a single host. (Either that or it won't allow the available capacity to drop below the RAM on a single host; I'm still not clear on which of these is really the case, since they're the same thing in my two-host cluster.) This has the net result that practically any amount of memory reservation is incompatible with what would otherwise seem to be natural settings for HA admission policy in a two-host cluster. Since Fault Tolerance forces memory reservations, that makes it similarly incompatible. I was told that if there were more hosts in the cluster, the reserved capacity would be "spread out" across more of them and some degree of memory reservation would be possible.

The net result for me is that I had to change my HA admission policy to reserve a percentage of the available resources (instead of "one host's worth") and calculate that percentage to exclude any memory reservations necessitated by the use of Fault Tolerance.