I had an issue recently where I needed to check the file space on an ESXi host. Luckily krypted.com landed in my Google search with just what I needed.
Most of us will be familiar with the df command. But in ESX, you use the vdf command, located in /usr/sbin. Running the vdf command will net you similar output to what you see with df. Simply run the following to see free space on each of your disks:
You can also list all of your data stores to correlate the vdf output with esxcfg: