I found this while browsing the documentation in the OPK disk. Though it was rather interesting because I can't find this on the Microsoft library for WHS 2011.
If you are using Windows Server Backup, it is not possible to back up a partition larger than 2190431223808 bytes. Therefore, it is recommended that the size of partitions on the server not exceed this value, particularly partitions that are used for data.
2,190,431,223,808 bytes. Over 2000 Terabytes. That's one heck of a lot of what ever you are storing on your home server. In only 1 partition. If that much video was loaded in one partition on the server, you could watch video 10 hours a day and it would still take 1/3 of a year to get through it all.
Its a lot.