- When enabled, this aims to transfer identical files only once to the Storage Platform by leveraging previous backups by other Accounts or the same Account.
- In addition, files included in the Backup Selection that are identical on the same volume are sent only once. However, this requires VSS to be enabled on the Backup Client.
The "transfer deduplication" phase (as indicated in the progress window during a backup) works as follows:
- Identify all files that must be processed for backup (by hashing all selected files and generating a preliminary index)
- Communicate with the Account's StorageServer to determine which files it hasn't received yet (by using their hashed values from the preliminary index)
- Start processing all files to ensure no changes have occurred in the meantime
- Send only the files identified in pt. 2 to the Storage Platform
This ultimately reduces the transfer size but also results in some files being processed twice on the disk thereby increasing disk activity during a backup.
Warning: When Backup Transfer Deduplication is enabled, partial backups (as with incomplete or interrupted backups) are no longer automatically purged on the Storage Platform unless the backup was successful. This is expected since transfer deduplication will leverage files from previous backups, including partial ones, to deduplicate transfers of subsequent backups. Purge partial backups manually from the Storage Platform Console if disk usage is adversely affected.
Enabling Backup Transfer Deduplication
Enable Backup Transfer Deduplication in the Backup Client's Options and Settings under the Performance page.
Interaction with Local Backup Copies
If local backups are also enabled, no deduplication occurs to the local backup destination.
Interaction with VSS
If VSS is disabled, identical files within the same volume will be sent separately and not be deduplicated.
To enable VSS, while in the Backup Client, open the Advanced page under Options and Settings.
Note: VSS does not apply to network shares.