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- Backup server. Schedules all backups and then records all the details in a database.
- Data mover server. Moves network traffic to attached backup devices, which are either disk or tape.
- SAN server. Runs on an application server; moves data for itself to attached backup devices, which are either disk or tape.
In enterprise environments, backup servers are responsible for scheduling thousands of backup jobs per day and committing thousands of associated backup details to the database; these activities are resource hungry.
So, best practice in an enterprise environment is to deploy dedicated backup and data mover servers, sized with enough memory and CPU to cope with the number of daily backup jobs, the amount of backup data and the number of backup devices. This has a cost implication, but ensures enough resources to cope with backup demand.
If dedicated servers are not a possibility and backup servers have to share with application servers, the question you need to ask is "Are there enough resources?" The answer is probably "no," but it comes down to the amount of risk you're exposed to in a situation where applications run from 9 a.m. to 5 p.m. while backups run from 6 p.m. to 8 a.m.
Often not factored in are the contradictory maintenance windows for backup and application servers. Maintenance windows for backup servers are usually during the day because backups take place outside of business hours. Maintenance windows for application servers are overnight as the applications run during the day. This leaves little or no time for maintenance or problem solving as the host can be busy 24 hours a day.
That may mean the following:
- You can't take down the application to fix any backup issues, but backups will fail until you do so.
- You can't perform backup maintenance at night as this is the backup window.
- Performing application maintenance on the server at night impacts backups.
- Failed backups have to be re-run during the day, consuming resources required by the application. This leads to the conundrum of whether or not to re-run the backups.
It's only when the consequence of not re-running backups results in data and financial loss that some businesses agree that dedicated backup servers are necessary. This scenario is avoidable if best practices are adopted and dedicated backup servers are deployed in the first place.
Conclusion: Always attempt to use dedicated backup servers. If this is not possible, make sure you identify the dangers of not doing so to senior management and get them to acknowledge your concerns.
This was first published in September 2010