In-file delta technology is an advanced data block matching algorithm with the intelligence to pick up changes (delta) of file content between two files. Using this algorithm, daily backup of large files over low-speed internet connection is made possible because it requires only the changes of information since the last backup to be sent over (assuming that the full backup of the file has been saved on the backup server already). This is what will happen in the backup of a 10 GB Outlook.pst file when it is backed up by the OBM with In-file delta technology:
- The whole file (10 GB) 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
- When the backup runs again later (sub-sequence backup), the 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.
- 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. (This delta file is assumed to be small because the content of PST files doesn.t change a lot during daily usage).
- Sub-sequent backups of this 10 GB Outlook.pst file will go through step 2 and step 3 again. As explained, only a small delta file and checksum file will be uploaded to the backup server.
- With In-file delta technology, daily backing up of large file over low-speed internet connection is now possible.
Incremental In-file delta Incremental Delta will facilitate ease of backup. The delta is generated by comparing with the last uploaded full or delta file. Delta generated with this method is smaller and uses the least bandwidth. However, for restoration, the full file and all deltas up to the required point-in-time are required to be restored and merged. For example: This is what will happen in the backup of a 10 GB Outlook.pst file with 100 MB increment each day. After the initial full backup, the backup application would continue to generate and upload delta instead of the full file until one of the following two rules are true:
- Number of delta files generated (since the last full backup) exceeded the [No. of Delta] setting.
- The delta ratio (ratio of delta file size against the full file size) exceeded the [Delta Ratio] setting.
With incremental delta, delta generated by comparing the current file with the last uploaded file (full or delta) is around 100 MB. Since the delta file size is about 100 MB daily, delta ratio of 1% would not trigger a full file upload. Instead, the OBM will continue to generate and upload delta files until day 102 (full file uploaded on day 1) when the number of deltas generated exceeds the [No. of Delta] setting. All delta files are generated with respect to changes made since the last incremental or full backup. This means that the last full backup file and ALL incremental delta backup files are required to restore the latest snapshot of a backup file. Differential In-file delta Differential Delta will facilitate ease of restore. The delta is generated by comparing with the last uploaded full file only. Delta generated with this method will grow daily and uses more bandwidth. However, for restoration, the full file and a single delta is required to be restored and merged. For example: This is what will happen in the backup of a 10 GB Outlook.pst file with 100 MB increment each day. After the initial full backup, the backup application would continue to generate and upload delta instead of the full file until one of the following two rules are true:
- Number of delta files generated (since the last full backup) exceeded the [No. of Delta] setting.
- The delta ratio (ratio of delta file size against the full file size) exceeded the [Delta Ratio] setting.
With differential delta, delta generated by comparing the current file with the last full file is about 100 MB for the 1st delta, 200 MB for the 2nd delta, and 300 MB for the 3rd delta (increment of 100 MB per day).
Since the delta file size increase by 100 MB per day, the OBM will continue to generate and upload delta files until day 52 (full file uploaded on day 1) when the delta ratio exceeds the [Delta Ratio] setting:
Delta file size of approximately 51 x 100 MB = 5.1 GB.
All delta files are generated with respect to changes made since the last full backup. This means that only the last full backup file and the last delta file are required to restore the latest snapshot of a backup file.
*In the event of corrupted delta file, only one particular snapshot of the file is non-restorable. All other snapshots with its delta would remain intact.
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