Differential backup
Also known as: differential backup vs incremental, cumulative backup
A differential backup saves everything that changed since the last full backup. Each differential grows over time because it always references the full backup, but restoring is simple: you only need the full backup plus the most recent differential.
- Saves all changes since the last full backup
- Restore needs only the full backup plus the latest differential
- Uses more space than incremental, but simpler to restore
How differential backups work
A backup plan starts with a full backup — a complete copy of the data. From there, each differential backup captures all changes made since that full backup, not since the previous differential. So every differential includes the previous day’s changes plus the new ones.
This makes differentials get larger as the days pass, until the next full backup resets the baseline. The upside is fast, simple restores.
Differential vs incremental
To restore from differentials you need only two pieces: the last full backup and the single most recent differential. With incremental backups you need the full backup plus every incremental in the chain, so restores touch more files.
The trade-off is storage and backup time versus restore simplicity: differentials use more space and take longer to run than incrementals, but they are quicker and safer to restore because there is no long chain to replay.