Backup model

This article describes the algorithm of the backup model.

CodeTwo Backup is Incremental Backup software designed for both Office 365 and on-premises Exchange servers. Incremental Backup means that only the initial cycle of a backup job backs up the whole mailbox content (Fig. 1.). Subsequent cycles are incremental, i.e. the software queries your Exchange server for changes in a desired mailbox since the previous cycle. If any changes are detected, only the modified (learn more) or new items are backed up again. The software does not back up the unmodified items again. This solution speeds up the whole process and saves disk space.

Additionally, CodeTwo Backup features item versioning. If during consecutive job cycles the software detects that the backed up content changed, the modified items are backed up again and stored together with the previous versions of the same items instead of overwriting the older versions (Fig. 1.). Thanks to this, during a restore job the user of the software is able to restore not only the most recent local copy of an item, but any previous version of it (assuming of course that there was more than one job cycle since the creation of this particular item).

Backup model - Incremental Backup
Fig. 1. Incremental Backup and item versioning. Unchanged items are not unnecessarily duplicated during cycles #2 and #3 - only new items are backed up in cycle #3. During cycle #4, a changed item is versioned to allow for restoring of the older copy in the future.

The backed up data is kept encrypted in a user-defined local drive location known as storage. The software user can configure multiple storages which can be either shared between multiple jobs or used exclusively by one particular job.

Backup jobs are what defines the scope of the backed up data. Similarly to storages, users can configure many jobs, for example to cover different sets of mailboxes, item types, age of backed up items, and so on (Fig. 2.).

Backup model - converging backup jobs
Fig. 2. Example of converging backup jobs.

Jobs run in cycles which consist of two phases: comparison and actual backup. As the name suggests, during the first phase the software communicates with the source server’s Exchange Web Services asking for the mailboxes’ folders and items' hashes. Those are compared to previously saved hashes to find out whether there were any changes in the mailbox or not. If the mailbox content changed since the previous cycle, the actual backup process starts.

Backup jobs can be divided into two types based on their continuity profile. There is a one-time backup (Fig. 3.) that goes through all user-specified mailboxes only once and stops. And there is a continuous backup (Fig. 4.) which runs constantly: the software goes through all user-specified mailboxes and, once finished, it starts all over again. To avoid excessively frequent backups in this mode, the user can define the so-called idle time in the job configuration wizard. This is a break the software will take before starting another cycle of a continuous backup.

Backup model - one-time backup
Fig. 3. One-time backup explained.
Backup model - continuous backup
Fig. 4. Continuous backup explained - note the repeated cycles and idle times.

Moreover, the program features a built-in scheduler which allows the software's user to customize job's activity periods even more (Fig. 5. and 6.). The scheduler can be configured separately for each job, for example to run one-time backup jobs of all mailboxes only on weekends and continuous backup jobs of the most important mailboxes during the working hours. Please note that the scheduler will automatically start a job at the beginning of a defined activity period, which makes the backup process seamless and fully automated.

Backup model - one-time backup scheduled
Fig. 5. One-time backup run by the scheduler within a defined activity period.
Backup model - continuous backup scheduled
Fig. 6. Continuous backup execution by the scheduler during an activity period.

See also

Creating backups - this article describes how to create a new backup job.

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