VMWare Error: “No space left on device” when powering up one specific host — even though there is space

In ESXi a vCPU will be mapped to a core on a real CPU core for computation. This means that a VM configured with 1 vCPU on a system with 4 cores can never use more than around 1/4th of the capacity of the system. Generally speaking, you do not want to configure VM's with too many vCPU's (as additional vCPU's adds overhead), nor too few (as you can not use the full capacity of the hardware).

For such a simple scenario as you describe you should not have to mess around with the resource allocation system or processor affinity. By default ESXi uses a system which assigns a fair share of resources to each vm, where configured resources are used to calculate how many shares a VM get. So you don't really have to worry about starvation.

There is a lot to learn about performance in ESXi, but I would recommend starting with reading through the best practices if you want to know how to configure the system for reasonable performance.

There are a few steps to check... but the first thing to try is a restart of the management agents. Gain SSH access to your standalone host and run: /sbin/services.sh restart at the prompt.