The following items describe the policies for the EZ-Snapshot service offered here at Rensselaer Polytechnic Institute:
- Scheduled snapshots occur every other day between the hours of 10:00pm and 3:00am. Snapshots are scheduled for every day of the week, with each computer having a Snapshot schedule of Mon/Wed/Fri/Sun/Tue/Thur/Sat. However, not all participants in the EZ-Snapshot service get backed up on the same date.
- Files get backed up incrementally. The system backs up only those files which have changed since the most recent version of the file was stored.
- The system stores up to two copies of a file. As a file changes, the system retains two versions of it. The system will retain the older version of the file for 30 days; after a file remains static for that length of time, the EZ-Snapshot system removes the older version, and stores only one version of the file in the system.
- The system retains files deleted from the host disk for 60 days. If a user deletes a file from his or her PC, the EZ-Snapshot version of the file will remain available for 60 days. After 60 days, however, the deleted file can NOT be restored. Files that remain on the host PC, remain in the EZ-Snapshot system.
- The EZ-Snapshot system will not store any files that get modified during the snapshot process. To ensure the integrity of the files stored in the EZ-Snapshot system, the system will not store any file(s) being modified during the EZ-Snapshot process. However, each PC system can control the number of times that a file copy gets retried when this situation occurs.
Users can set the CHANGINGRETRIES parameter in the dsm.opt file on their PC system to control the number of retries.
Active vs. Inactive Backup Versions
As an example of what we mean by "active" and "inactive" versions of a file, let's say that you create a new file on your workstation, and an Incremental (complete) backup is performed on Tuesday at 11pm. This file is then stored as the active version.
When another Incremental (complete) backup is performed on Thursday, TSM uses that active version to compare the file with your workstation to see if the file has changed since the previous backup. If the file has changed, it is backed up again. The newest backup version from Thursday then becomes the active version, and the file from Tuesday is marked as the inactive version. Just remember: The most recently backed up version of the file is always the active version, as long as it still exists on the workstation and as long as you use the Incremental (complete) backup option.
If you delete a file from the workstation, TSM will detect this the next time an Incremental (complete) backup is performed, and will now list all backed up copies of that file as being inactive. The inactive file remains on the TSM server for 60 days, and is then deleted