I've recently taken over a SQL Server database that didn't have any transaction log backup routine running for at least 2 years. The first log backup was very large (3.8 gb on a 1.14 gb database) as you would predict, however subsequent log backups are still larger than I would have expected (somewhere in the region of 3 mb).
I also restored the database to a QA and ran several sequential log backups without there being any activity on the database and the log file backups were still ~3 mb.
What would account for the size and consistency of the transaction log backups with nominal activity on the database itself?
Here is the script we're using to run the TLOG backups, this is being executed every 10 minutes:
BACKUP LOG [mydatabase] TO DISK = @fullpath WITH RETAINDAYS = 2 , NOFORMAT , NOINIT , NAME = @bckName , SKIP , REWIND , NOUNLOAD , STATS = 10;