An administrator is attempting to power on a virtual machine with 32GB of memory. The operation fails with the following error: - Could not power on VM : No space left on device - Checking the space o

When a VM powers on, ESXi creates a .vswp swap file sized at (configured memory - memory reservation); with 32 GB RAM and zero reservation, a 32 GB swap file is required but only 30 GB is free. Setting a 2 GB reservation reduces the required swap file to 30 GB, exactly matching the available space and allowing the VM to power on successfully.

Mounting the vmdk on another VM and freeing space on that VM's files would not increase the free space on the original datastore where the swap file needs to be created.

vSphere HA admission control manages cluster-level failover capacity reservations and has no effect on the per-VM swap file that must be created at power-on time.

A memory limit caps runtime memory consumption but does not reduce the size of the swap file that ESXi must allocate at power-on, so the 'no space left on device' error would persist.