Knowledge Base

SQL Backup mirrored backups

Category: Troubleshooting & error messages
Date: 05 Jun 2009
Product: SQL Backup
Are mirrored backup written in parallel and what is the impact on the system, for example i/o load; processor load and do the i/o's incur waits (will the backups finish at the same time even if one device is twice as fast as the other)?

Mirrored backups are written in parallel and the backups will finish at the same time. So the backup location should have similar properties (same number of the backup devices, performance characteristics etc).

As far as processor load is concerned, the mirror file doesn't have much of an impact on performance because the compression and encryption are done only once; it is just the writing which is done in parallel.

The only thing one should keep in mind is that if one of the backup devices is slow then overall process will be slow so you will be putting load on your SQL Server for a longer period. So ideally, if the backup devices are not of similar characteristics then backup locally to the fastest device and then just use COPYTO to copy the files to other locations.