Mirroring and its effect on the physical log

The physical log is write intensive, with activity occurring at checkpoints and when buffered data pages are flushed. I/O to the physical log also occurs when a page-cleaner thread is activated. If the dbspace that contains the physical log is mirrored, you encounter a slight double-write performance penalty.

For details on the slight double-write performance penalty, see Consider mirroring for critical data components.

To keep I/O to the physical log at a minimum, you can adjust the checkpoint interval and the LRU minimum and maximum thresholds. (See CKPTINTVL and its effect on checkpoints and BUFFERPOOL and its effect on page cleaning.)