A basic problem that remote and mobile users face today is connecting to storage management services by using modems with limited bandwidth or poor line quality. This creates a need for users to minimize the amount of data they send over the network, as well as the time that they are connected to the network.
To help address this problem, you can use subfile backups. When a client's file has been previously backed up, any subsequent backups are typically made of the portion of the client's file that has changed (a subfile), rather than the entire file. A base file is represented by a backup of the entire file and is the file on which subfiles are dependent. If the changes to a file are extensive, a user can request a backup on the entire file. A new base file is established on which subsequent subfile backups are dependent.
This type of backup makes it possible for mobile users to reduce connection time, network traffic, and the time it takes to do a backup.
Assume that on a Monday, a user requests an incremental backup of a file called CUST.TXT. The user makes daily updates to the CUST.TXT file and requests subsequent backups.
| Version | Day of subsequent backup | What Tivoli Storage Manager backs up |
|---|---|---|
| One | Monday | The entire CUST.TXT file (the base file) |
| Two | Tuesday | A subfile of CUST.TXT. The server compares the file backed up on Monday with the file that needs to be backed up on Tuesday. A subfile containing the changes between the two files is sent to the server for the backup. |
| Three | Wednesday | A subfile of CUST.TXT. Tivoli Storage Manager compares the file backed up on Monday with the file that needs to be backed up on Wednesday. A subfile containing the changes between the two files is sent to the server for the backup. |