I have a database on a SQL 2008R2 server running (virtual) Windows 2008R2 - all 64 bit - all current with service releases. The database is in full recovery. There is a full backup performed every evening at 9 PM. Transaction logs are backed-up every hour beginning at 8 AM and ending at 6 PM. There is generally no one using the accounting application that utilizes the database after 6 PM and definitely no one between the hours of 9 PM and 6 PM. There are a couple of stored procedures in another database that read data from this database during the evening - but no writes. With all this the log file routinely grows to more than two GB's during the evening so that the first transaction log backup at 8 AM is very large while the one's that are created each hour range between 10 and 150 mb.
Unable to solve this riddle, I asked and received more disc space in the form of a second logical drive to store the backups so I would not consume all the space on the main disc inadvertently. Much to my surprise, when I did this the problem went away. None of this makes any sense. If there was some activity going on at night that I had missed I would still have the problem. Nothing else has changed. What am I missing?