Backup Methods
Two main factors govern backup operations:
- Frequency
- how often to backup
- configuration reflects how much lost work can be tolerated
- Retention
- how long a backup is kept
- short-term and long-term
Backup Chains
Requirements for backup frequency and retention must be managed against:
- capacity of the backup media
- time it takes to complete a backup job
These requirements are managed by using different types of jobs in a backup chain.
Main Types of Backups
| Type | Data Selection | Backup Job Time and Storage Requirement | Recovery Complexity | Archive Attribute |
|---|---|---|---|---|
| Full | All selected data regardless of when it was previously backed up | High | Low (single job) | Cleared |
| Incremental | New files and files modified since last backup job | Low | High (multiple jobs) | Cleared |
| Differential | New files and files modified since last full backup job | Moderate | Moderate (two jobs) | Not cleared |
Info
Windows uses an archive attribute to determine the backup status. Linux doesn’t support a file archive attribute. Instead, a date stamp is used to determine whether the file has changed. Most software also has the capability to do copy backups. These are made outside the chain system (ad hoc) and do not affect the archive attribute.
Synthetic Backup
A synthetic full backup is not generated directly from the original data but instead assembled from other backup jobs.
- option for creating full backups with lower data transfer requirements
How it Works
- The chain starts with an initial full backup as normal and subsequently makes a series of incremental backups.
- When the next full backup is scheduled, the backup software makes one more incremental backup. It then synthesizes a new full backup from the previous full and incremental backups.