I have a large database in Simple recovery model (vendor requirement) and it took 3 days to back it up to the new hosting company's server.
The morning of the third day, the DB went offline because the transaction log had filled up its drive.
My understanding was that SQL Server would just start recycling the space. What's more interesting is that I don't think the database started working again until I gave it a bit more space - it stayed busted after the backup was complete. I didn't take the time to properly debug, though, so I don't know exactly why it was stuck.
Question: Why can't SQL Server in Simple Recovery re-cycle its transaction log while it is backing up?