Some quick math:
NTFS default large disk cluster size is 4,096 bytes (4 KB).
Theoretical 2^64 clusters:
4096 * 2^64
= 4096 * 18446744073709551616
= 75,557,863,725,914,323,419,136 Bytes
= 73,786,976,294,838,206,464 Kilobytes
= 72,057,594,037,927,936 Megabytes
= 70,368,744,177,664...