Differential backups are large even with delta backup switched on. How to make backups smaller and faster?
If differential backups with “Delta incremental backup”” switched on are too large, you can lower the value of the advanced setting “Split file size” from 10240 kB (10MB) to approximately 1024 kB (1 MB) or even to 256 kB (0.25 MB). With that setting and small changes to large files (databases, mail files) backups will be small (2-25 MB on average) and will be completed much faster. You need to remember, however, that once this setting is changed, the two following backups will be full. This is due to the fact that the software will have to recalculate checksums of all fragments. Only on the third backup will the (often considerable) difference be noticeable. Large incremental backups may also be caused by an incorrect backup scope (temp files not excluded). Slow backups may also be caused by incorrect settings of the antivirus scanner.
