The four backup types
Full, incremental, differential and mirror: what each run writes, what a restore reads, and which to choose.
On this page
The Backup type on the wizard's Settings step decides what each run writes to the destination. There are four; they differ in size, speed, and how many sets a restore reads. New jobs start as Incremental.
The four at a glance#
| Type | Each run writes | A restore reads | Edition |
|---|---|---|---|
| Full | everything | one set | every edition |
| Incremental | only what changed since the last run | the full set and every set after it, up to the point you chose | every edition |
| Differential | what changed since the last full | two sets at most | Home and Pro |
| Mirror | what changed; the rest moves over from the previous copy, which is then removed | the one copy | Home and Pro |
Full#
Every run copies every file. Each set stands alone, so it is the simplest to reason about and the largest: ten runs of a 50 GB folder hold about 500 GB, less what compression and identical-file detection save. Good for small, precious folders, and for jobs that run weekly or less.
Incremental#
The first run is a full. Every later run stores only the files that are new or changed since the run before. A nightly job on a 50 GB folder where 300 MB changes a day adds about 300 MB a night. To restore a point, the app reads the full set and each set after it up to that point; you pick a date and GBM AI does the rest.
This is the type for anything that runs daily or more often.
Differential#
Like incremental, but each run stores what changed since the last full. Sets grow until the next full, and a restore needs two sets at most. Useful with a weekly full and daily differentials, or on a destination that is slow to read many sets.
Mirror#
A copy on the destination that always matches the source. The first run writes a complete copy. After that, each run reads and writes only the files that are new or changed; the copies of the files that did not change move over from the previous mirror into the new one, and the previous mirror, left with only the old versions, is then removed. The drive needs room for one copy and what changed, not for two copies, and a run of a large folder where little changed takes minutes instead of hours.
There are no older versions and no retention to set. A file you deleted on Tuesday is gone from the mirror after Tuesday night's run.
A file the run cannot read (in use, under a folder it cannot open, or online-only and not downloaded) keeps its last copy in the new mirror; the run's report lists it and says so.
Should a run stop, fail or be cut short by the PC turning off, every copy it moved goes back into the previous mirror, which is whole again and restores as before. The same happens, with The mirror was not updated. The previous copy is kept whole. (E-SET-007), in the rare case where the previous mirror holds the only good copy of a file the new one could not store or check. While a run moves copies, the previous mirror cannot be restored from; restore from the new one when the run finishes.
Run as full writes a whole new copy beside the previous one, which needs room for both; so does the run after one that was not updated (E-SET-007). GBM AI checks first and says so before writing anything when there is not enough: There is no room for a second copy while the mirror is written. The previous copy is kept. A mirror in a bucket writes a whole copy on every run.
Important
A mirror cannot give back last week's version of a file. If that could ever matter, use incremental.
Chains#
A full set and the incremental or differential sets that build on it form a chain. Retention removes whole chains only, and never the newest one. On the Restore page, the Last 14 days strip draws full sets dark and the others light, so the chains are visible. On Home and Pro, start a new full after N runs on the Settings step decides how long a chain gets.
Changing the type later#
You can change the type of an existing job. From the next run the job uses the new type: an incremental builds on the newest set already on the destination, a differential on the newest full. The sets already there stay restorable.
Two changes do start again with a full: switching encryption on or off, and changing the password. Switching to Mirror warns first: Switching to a mirror removes this job's earlier restore points once its next run completes.
Run as full, once#
Run as full in a job's ⋯ menu runs one full backup without changing the job. Useful before a long trip or after a big reorganisation of the source.