Index maintenance usually starts 3 hours before the database full backup and ends before the full backup start.
The database is using the Simple Recovery model.
Last weekend the index maintenance took more than 5 hours and the full backup was running at the same time.
We have noticed that since the full backup started the transaction log File started to grow every 30 Seconds until it filled the disk and both full backup and maintenance failed due to insufficient disk space for log file.
Why, when the backup has started while index reorganize is running, does this happen to the transaction log file?