I agree with Gail, you should be backing up to a separate disk or raid group/set of spindles, disable SQL backup compression, then use Backup Exec 2012 to do data deduplication and store it on tape. I'm assuming the tape backup is the performance bottleneck.

You should first test the theoretical max backup performance by writing to the NUL device.

Adjust the BUFFERCOUNT and MAXTRANSFERSIZE (1MB) and BLOCKSIZE.

-- Try different MAXTRANSFERSIZE

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 25, MAXTRANSFERSIZE = 524288

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 25, MAXTRANSFERSIZE = 1048576

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 25, MAXTRANSFERSIZE = 2097152

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 25, MAXTRANSFERSIZE = 4194304

--Try different BUFFERCOUNT with best MAXTRANSFERSIZE

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 10, MAXTRANSFERSIZE = 2097152

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 40, MAXTRANSFERSIZE = 2097152

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 100, MAXTRANSFERSIZE = 2097152

--Try different BLOCKSIZE

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 100, MAXTRANSFERSIZE = 2097152, BLOCKSIZE = 1024

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 100, MAXTRANSFERSIZE = 2097152, BLOCKSIZE = 16384

BACKUP DATABASE [dbname] TO DISK = 'NUL' WITH STATS = 10, BUFFERCOUNT = 100, MAXTRANSFERSIZE = 2097152, BLOCKSIZE = 65536

Once you find the max possible speed, backup to mulitple files on a raid or SSD.

Good example here:

http://henkvandervalk.com/how-to-increase-sql-database-full-backup-speed-using-compression-and-solid-state-disks

Im backing up a 250GB database in around 12 minutes. Max backup speed was 340MB/sec with Raid5 disks using NUL device and 280MB/sec with 8 backup files.