Sql-server – How to backup the transaction log for a mirrored database in SQL Server

Frankly, there's no reason NOT to run Transaction Log backups at a much more frequent rate. A transaction log backup doesn't HURT anything. (In MOST scenarios it's just going to take a bit of CPU and disk activity - but it's typically almost negligible.)

Moreover, you can both increase your coverage AND boost performance by moving log-file backups to less performant disk: SQL Server Magazing: Maximize Storage Performance

By increasing frequency of your backups, you'll decrease your window of potentially lost data. (Technically, if SQL Server crashes you can sometimes recover lost transactions since the last FULL/DIFFERNTIAL backup IF your log file is still intact. But usually, if something has gone wrong enough for you to be backing up in the first place, there's a DECENT chance your log file is gone/toast.)

Feel free to check out the following videos for a bit more background and information on what's going on in terms of backups, logs, and best practices:

SQL Server Backups Demystified

SQL Server Logging Essentials

Managing SQL Server 2005/2008 Log Files

SQL Server Backup Best Practices

Nope - it definitely doesn't. The only thing that allows the log to clear/truncate in the FULL or BULK_LOGGED recovery models is a log backup - no exceptions. I had this argument a while back and posted a long and detailed blog post with an explanation and a script that you can use to prove it to yourself at Misconceptions around the log and log backups: how to convince yourself.

Feel free to follow up with more questions. Btw - also see the long article I wrote for TechNet Magazine on Understanding Logging and Recovery in SQL Server.

Thanks