Backup strategies are not just about choosing between full, incremental and differential backups. A well-planned backup strategy and restore strategy maximizes data protection and includes backup frequency, retention, automated backups, and resource management to ensure data availability.
This article first explains the differences between incremental and differential backups and then describes how to integrate them into a structured backup strategy.
Understanding Incremental and Differential and Full Backups
Full Backups copy everything that needs to be backed up. They are the simplest way of doing backups, but at the same time, they consume a lot of resources.
Incremental and differential backups both reduce the amount of data that needs to be backed up compared to full backups. The difference lies in how they track and store changes.
Full Backups
Full backups save all the data on the source filesystem.
- Full backups are usually performed in relatively long intervals.
- The data of the Full backups may only be overridden after the desired data history has passed.
- Since all data is stored, Full backups consume a lot of storage space and are slow to perform.
Incremental Backups
Incremental backups save only the data that has changed since the last backup, whether full or incremental.
- Incremental backups must be performed most frequently, for example daily.
- The data from such backups may only be overwritten after the time that a daily resolution of changes is required to be available. Since only changed data is stored, they require less storage space and are faster to perform.
However, restoring from incremental backups takes longer, as it requires the last full backup and all subsequent incremental backups. If one backup is missing, data recovery may fail.
Differential Backups
Differential backups save all data that has changed since the last full backup.
- Differential backups are performed in a greater interval than incrementals. Often this interval is a week..
- The data from such backups may only be overwritten after the defined time has passed, that a weekly resolution needs to be available for the backpups.
- Restoring is faster than only with incremental backups because only the last full backup and the most recent differential backup are needed.
Over time, differential backups grow larger since they store all changes made since the last full backup.
Building a Backup Strategy
Choosing between full, incremental and differential backups is only part of the backup concept. A structured backup plan also defines when backups are performed and how long data is retained.
A possible concept looks like this:
- Incremental backups: Daily, retained for at least three weeks.
- Differential backups: Weekly, retained for at least three months.
- Full backups: Monthly, retained for at least one year.
We will make one small change to this schedule: to give backups more time at weekends, we do without the daily backup on Saturday and start the full and differential backups on Saturday instead of Sunday.
Implementing the Strategy in Bareos
In Bareos, implementation requires two steps:
- The backup type and interval are determined by one resource.
- The storage time is determined by another resource.
Next to the backup type and interval, the backup concept also describes how long the data will be kept. Once the storage time is over, the data can be overwritten.
To apply different storage times for incremental, differential and full backups, Bareos uses separate storage pools for each backup type. This ensures that retention policies are followed without interfering with other backups.
Summary
- Incremental backups must be performed most frequently, usually daily, stored for multiple weeks and require the last full backup plus all incrementals for restoration.
- Differential backups must be performed in a longer interval, usually weekly, stored for at multiple months and require only the last full backup and the latest differential backup and all newer incrementals for restoration.
- Full backups must be performed in longer time intervals like monthly and stored for as long as old data needs to be restorable, for example one year.
- Backup intervals and storage times are managed separately in Bareos.
- Dedicated storage pools ensure retention policies for different backup types.