Re: ESXi 5 Insufficient disk space on datastore

You wont be able to shrink the disk again in situ.

Whats happening is that when you try to power on the VM, its trying to create a 12GB backing file for your memory.

You can:

1) Storage vMotion this or some other VM to a different datastore, freeing up space

or

2) Give this VM a 100% reservation on its memory, and it wont try to create that file.  It should boot then (but your datastore will still be full...)

or

3) Use VMware Converter to export the VM to a local disk, then back, which can thin out the disk.

#1 is by far the best option.