You posted this in mirroring forum, so if mirroring is actually set up you can use the monitor gui for that to see how backed up things are.
Also, a VERY VERY common problem is people having databases in FULL recovery mode but not doing any form of TLOG backup. A FULL backup will NOT flush committed transactions from the tlog!!!
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru at GMail