Full, differential and incremental backups trade storage and backup time against restore time. The right mix depends on how big your data is, how fast it changes, and how quickly you need it back.
The three types at a glance
| Full | Differential | Incremental | |
|---|---|---|---|
| Contains | Everything | Changes since the last full | Changes since the last backup of any type |
| Size over a week | Same every time | Grows each day | Small each day |
| Backup time | Longest | Medium, growing | Shortest |
| To restore you need | 1 file | Last full + last differential | Last full + every incremental since |
| Risk | Lowest | Low | One damaged file breaks the chain after it |
A worked example
Take 50 GB of data where about 2 GB changes per day, with a full backup on Sunday:
- Daily full: 7 × 50 GB = 350 GB per week. Restore any day from one file.
- Sunday full + daily differential: the differentials grow roughly 2, 4, 6, 8, 10 and 12 GB through the week. That's about 92 GB in total. Restoring Friday needs Sunday's full and Friday's differential.
- Sunday full + daily incremental: six files of about 2 GB each, about 62 GB in total. Restoring Friday needs Sunday's full and all five incrementals, in order.
Real differentials grow more slowly than this when the same data changes repeatedly. Try your own numbers in the backup storage calculator.
How SQL Server names these
SQL Server has full, differential and transaction log database backups. It has no backup type called "incremental". Transaction log backups play that role: each one holds the log records since the previous log backup, and together they let you restore to any point in time. They need the FULL recovery model.
| Goal | SQL Server pattern |
|---|---|
| Small database, losing up to a day is acceptable | Daily full, SIMPLE recovery |
| Larger database, backup window is tight | Weekly full + daily differential |
| Can lose at most minutes of data | Weekly full + daily differential + log backups every 15 to 60 minutes, FULL recovery |
One trap: a manual full backup taken in the middle of the week becomes the new base for later differentials. If that file is deleted or moved, the following differentials are useless. Take ad-hoc copies WITH COPY_ONLY, as shown in how to back up a SQL Server database.
For files and folders
File backup tools decide what changed using file modification times or the Windows archive attribute. The same trade-offs apply. Incrementals are small and quick; differentials are simpler to restore.
Which should you choose?
- Daily full backups are the simplest and the safest when the data fits your backup window and storage.
- Add differentials when full backups take too long or use too much space. Restores stay two-step.
- Use incrementals (or SQL Server log backups) when you need frequent restore points. Pair them with regular fulls and restore tests, because the whole chain has to be intact.
Whatever you pick, restart the chain with a new full backup regularly, weekly for most small businesses. That keeps restores short and limits the damage one bad file can do.
Backup types in Velocity
Velocity lets you choose full, incremental or differential for each backup job, for SQL Server databases and for files and folders, and schedule each job daily, weekly, monthly or on an Nth weekday.