2010 R3 - backup to Disk and deduplication

I have a 1.8 TB disk on the san that the backup server can access, but the job I want to run is about 3 TB of data for a full backup. How do I get the job to run on another disk after the first disk fills up since I cant go over 2 TB of disk space (windows limitation I think)? Also, If the full backup job is about 3TB and I need to to have enough space for a month of full backups every weekend and incrementals during the week and take a full backup at the end of the month and put it on tape for off site storage - how much space woudl I need? I'm using 2010 R3 on W2K8 R2 Thanks.