The space required for a backup is highly variable. It depends on the number of servers includes in the backup and the data sets selected. However, the largest and most significant backup is that required for voicemail.
The following tables show the potential space required for a worst case full backup. That is, one that assumes all the users have used their voicemail mailbox and other facilities to their maximum capacity.
The minimum disk size column indicates the disk hard disk size required to have a sufficiently large backup quota (see above) for at least one maximum full backup.