Why is SQL Server backup so much larger than the DB files?

I have a SQL Server DB that is about 13Gb with a 1.6Gb log file. When I back it up, however, it creates a 50Gb .bak file! Why is that?

I have read some commentary here about transaction logs, but my DB runs on my laptop and there is no DB activity during the time of the backup. (It only takes 5 minutes).

My backup type is Full, my recovery type开发者_运维问答 is Full, and I am doing Copy-Only backups. Any ideas? Much appreciated!

I am using SQL 2008 R2, Developer Edition.

It might be because the backup routine is appending the new backup to the same file?

There is an option in the Backup dialog in Sql Management Studio to Append or Overwrite all existing backup sets. If you have Append if will add the backup to the same .bak file and the .bak file will be larger for every backup.

In Transact Sql it is the INIT and NOINIT option which determine if the bak file is overwritten or appended.

In my case, I found that the 500MB database also had a 560MB full text catalogue attached which gets included in the backup file. I thought I'd add this despite another answer having been accepted in case anyone else is still stumped :)

In my case, heavy use of filestream objects made for the largest part of the backup file.