Incremental Backup

As the name indicates, this is backup in increments. An incremental backup makes a copy of all the files that were changed after the last backup.

Let’s say we have File A, a word processing document. File A was backed up during a full backup on Monday. Then someone updated the document on Tuesday. An incremental backup would copy File A and any other file that was modified on Tuesday and nothing else. It only backs up the files that were modified since the last backup.

What happens if a fire hits the server room and files have to be restored? Both Monday’s full backup and Tuesday’s incremental backup would be used to restore all the files to their most updated versions.

Another example:

Monday: Files A + B + C are backed up (full backup).

Tuesday: File A is modified. File A is backed up (incremental backup).

Wednesday: File B is modified. File B is backed up (incremental backup).

Thursday: Files A and B are modified. Files A + B are backed up (incremental backup).

Let’s say that the fire struck on Friday instead of Tuesday, destroying everything. So you would have to use Monday’s full backup plus the backups of all the other days in order to restore everything. This would mean accessing at least four backups before finally getting everything restored.

Of the three main backup types, incremental is the one that uses the least resources. If tape is being used to record the backups, then the incremental ones will use the least tape. Depending on the size of the backups, a single tape could be used for several incremental backups. However, several tapes may be necessary for a single full backup. If incremental backups are being stored on a CD or hard drive, they will take up much less space than full backups.

However, of the three main backup methods, the incremental method is the one that takes the most time when an entire system needs to be restored.

Isn’t there another choice besides making a humongous full backup or making many little incremental backups? Yes, there is.