Explanation
According to the Create machine catalogs document from Citrix Virtual Apps and Desktops 7 2308, MCS adds the machines to Active Directory, which creates unique identities. MCS creates the number of VMs specified in the wizard, with two disks defined for each VM. In addition to the two disks per VM, a master is also stored in the same storage location. The identity disk is one of the two disks per VM, and it is used to store the Active Directory identity and other unique information for each VM. The identity disk is 16 MB in size and is created for each VM regardless of the disk type selected for the catalog.