I have a customer with a 6GB database. They process approximately 200 sales transactions per day. After 24 hours they run out of storage space because the log file has gone from 0MB to 100GB. So every day I set the Logging method to SIMPLE. I then shrink the log file. I then set logging back to FULL. I then take a full backup and a log backup for good measure - both execute happily. Now the log file is 0MB. 24 hours later log file is 100GB again. There are no open transactions at any stage (I checked before and after). When I select log_reuse_wait_desc from sys.databases I get log_reuse_wait_desc=LOG_BACKUP.
What is causing the log file to go crazy and fill up the drive?