Hi,
Yes, ACS 5.0 and 5.1 will require 500Gb of hard disk space configured in the ESX virtual machine for it to install and run correctly. This initial design reflects the hard disk specification of the ACS 5.x appliance. The product team understands that this requirement may seem excessive to many customers. Loosening this requirement will be under consideration for future ACS 5.x releases.
HTH
JK
~Jatin