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In-File Delta technology


With In-File Delta technology, it is now possible to backup very large files daily. 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. Both client-side backup applicants, StorageVault™ Server Backup Agent(SBA) and StorageVault™ Desktop Backup Agent(DBA), are equipped with our proprietary In-File Delta technology. With this feature, the original file is required to be backed up once only, i.e. in the first backup job. Subsequently, only changes are necessary to be backed up. There are two types of In-File Delta that users can choose.

1 Differential Delta Mode
“Differential Delta” will facilitate ease of restore. The delta is generated by comparing with the latest uploaded “Full” file so the delta file can grow daily and uses 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.
All delta files are generated with respect to changes made since the last full backup file (i.e. differential backup). It means only the last full backup file and the last delta file are required to restore the latest snapshot of a backup file. Other intermediate delta files are only required if you want to restore other snapshots of a backup file. Differential in-file delta backup has the benefits that a corrupted delta file would only make one particular version of a backup file non-recoverable and all other backups created by other delta files of the same file would still be intact.

2 Incremental Delta Mode
“Incremental Delta” will facilitate ease of backup. The delta is generated by comparing with the latest uploaded “Full” or “Delta” file so the delta file is the smallest 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.
All delta files are generated with respect to changes made since the last incremental backup. It means the last full backup file and ALL incremental delta backup files are required to restore the latest snapshot of a backup file.

The major differences are summarized in the following table:
In-File Delta Technology
Pros
Cons
Differential Always use the latest uploaded “Full” file to generate the delta file.
For restore, just need the
full and a delta to recover to aspecific point-in-time.
The daily delta file will be larger than incremental delta and needs more bandwidth to upload.
Incremental Always use 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.

3 Delta Generation
The delta is generated by extracting the differences between the latest file to backup and the original file stored on the server. Both files are divided into individual blocks using the same block size and the blocks compared to determine whether they’re the same or different. The differences are extracted into the delta file.

generate-delta-file

4 Block Size Setting
Using a different block size setting can affect the speed of generation and size of the generated delta. Generally speaking, the relationship between the block size setting and the delta generated is as follows:
- The smaller the block size, the delta file generated will be smaller but takes longer to process.
- The larger the block size, the delta file generated will be larger but is faster to process.

The block size setting available are Auto, 1K, 2K, 4K, 8K, 16K, 32K, 64K, 128K, 256K, 512K and 1M. With “Auto”, the block size used will be initially set using the backup file size according to the table below:
Initial Full File Size
Auto Block Size Used
> 15G
64K
> 8G ≤ 15G
32K
>2G ≤ 8G
16K
>500M ≤ 2G
8K
≤500M
4K

5 During Backup
Assume the initial full file is 100MB and grows daily by 10MB. The files uploaded to the server and the approximate storage space required is as follows:

daily-upload-to-server 2

6 During Restore
Assume restoring the various files backed up above.

files-downloaded-from-MRS-to-restore 2

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