Are you backing up to Tape or a VTL? If backing up to tape, I would look at the number of objects being backed up, and, in the Drive Properties in the Destination tab of the Backup Specification, and find out what your Concurrency is set to (for VTL, it should be set to '1')
Physical tape drives need a lot of Data fed to them, otherwise, when the tape buffer empties, the drive will stop wait for the Tape Buffer to fill, reposition the tape, and start writing again. For physical tape drives, we normally recommend that consurency be set to 10 or 12, which is the amout of data streams being to the device at one time, and will normally keep teh tape buffer filled.
Of course, if you don't have enough Data Streams to meet the concurrency, there is not much that can be done about this
The other thng I can recommend is to add a couple of lines to the 'omnirc' file on your media agent. The 'omnirc file does not exist by default, if you don't have one, it can be created using Notepad on Windows systems, or by using the UNIX 'touch' command
touch /opt/omni/.omnirc
Windows 2003
Program Files -> Omniback -> omnirc
Windows 2008
Program Data -> Omniback -> omnirc
I wrote a support tip on the use of the 'omnir' file if you want to learn more
Add these lines
OB2IPCNOSENDRECVLOOP=1
OB2SHMIPC=0
Save the file. On Windows, make sure the filename has no extension, like 'txt' or 'tmpl'. Also, on Windows, after editing the 'omnirc' file, you must stop and restart the DP INET service on the system where you did the editing
I have attached a Whitepaper that discusses Performance issues