Snapshot .vmdk files contain metadata (grain tables, ...) which requires additional disk space, so the size of the snapshot .vmdk file could become larger than the original virtual disk file. In order to be able to take snapshots with current vSphere versions (this changes with ESXi 5.5) the maximum virtual disk size is 2,032GB (see table "Calculating the overhead required by snapshot files" at VMware KB: Creating a snapshot for a virtual machine fails with the error: File is larger than maximum file size sup…)
André