In-File Delta Technology

In-file delta technology is an advanced data block matching algorithm which analyses changes (delta) in content between two versions of the same file. Using this algorithm, daily back up of large files (e.g. a 10GB Outlook.pst file) is possible because it requires only those parts of a file that have changed to be sent.

How In-file delta technology works

The following occurs when a 10GB Outlook.pst file is backed up by OBM utilising in-file delta technology:

  1. The entire file (10GB), along with its checksum file, are backed up to the backup server. This can be done directly through the internet or indirectly using the seed loading utility on a removable hard disk.

  2. When a backup is run at a later date, OBM will download a checksum listing of all data blocks of the full backup file (or last incremental backup file) from the backup server and use it to pick up all changes that have been made to the current Outlook.pst file.

  3. Changes detected are then saved in a delta file which is uploaded to the backup server. A new checksum file is generated and is also uploaded.

  4. Subsequent backups of this file will go through step 1 and step 2 again. Only a small delta file and checksum file will be uploaded to the backup server.

  5. With in-file delta technology, daily backup of large files over a low-speed internet connection is now possible.

In-File delta modes

There are two different modes of operation available (“Differential” and “Incremental”) for In-File Delta backups.

Both modes will use approximately the same amount of disk space storage on the server.

Differential delta mode

“Differential Delta” will facilitate ease of restore. The delta is generated by comparing the latest uploaded “full” file so the delta file can grow daily and use more bandwidth during backup. For restoration, the full file and a single delta file is required to restore the file to a specific point in time.

Incremental delta mode

“Incremental Delta” will facilitate ease of backup. The delta is generated by comparing the latest uploaded “Full” or “Delta” file so the delta file is as small as possible and uses the least bandwidth during backup. For restoration, the full file and all delta files up to the required point-in-time is required to restore the file to a specific point in time.

The major differences are summarised in the following table:

In-File delta technology Pros Cons
Differential - Always uses the latest uploaded “Full” file to generate the delta file. For restores, just need the full and a delta to recover to a specific point-in-time. The daily delta file will be larger than incremental delta and needs more bandwidth to upload.
Incremental - Always uses the latest uploaded file (whether “Full” or “Delta”) to generate the delta file. Daily delta file only shows the difference between the current file and previous upload file. The incremental delta file will be smaller than the differential delta file and so should upload faster. For restore, need to use the full and all deltas up to the point-in-time to recover to a specific point-in-time. If any delta file is corrupted, the file can only be recovered up to the point-in-time before the corrupted delta.

You can read more about In-File Delta technolog in our documentation section.