Exchange MBdata file

The folder named MBdata file in exchange generates an unusual number of log files over the weekend. Approx 2.5 gig happen over the weekend. I know a standard backup clears the files during the week but so many are generated prior to the weekend backup the Public Store and the Mailbox Store become dismounted. When this happens the back-up fails to clear the files
Any ideas what to do?

john kish