The retention status of a save set and the recycling status of a storage volume indicate how ISM manages your data. A save set can consist of storage-space backups or logical-log backups. To see the status of a save set, use the ism_show -volume name command. For more information, see ism_show.
The ISM server tracks your data based on the retention period that an administrative user sets. For details, see Setting the Retention Period for All Data. Every time that a backup is completed, the ISM server creates entries for each backed-up save set in the ISM catalog. The ISM catalog allows ON–Bar to reconstruct the data to look exactly as it did at a specific time.
Retention, expiration, recycling, and labeling are volume-level operations.
The retention policy applies to both volumes and save sets. ISM retains the volume until all the save sets on that volume expire. A volume expires when the newest save set stored on the volume expires. If a volume is empty, it expires when its expiration date is reached.
For example, if you set the retention period to one month, an empty volume expires in one month. Suppose you save a save set to this volume each week until it holds six save sets. This volume expires after 10 weeks, one month after the last save set is saved during the sixth week.
ON–Bar can restore a save set any time during the retention period. To determine if ON–Bar can restore a specific save set, use ism_show -volume name to check the save-set status. If the retention status of the save set is blank, the retention period for the save set has not yet expired, and ON–Bar can restore it. For information on using ON–Bar, refer to the IBM Informix: Backup and Restore Guide.
If the retention status of a save set is marked Expired, ON–Bar can no longer restore the save set. You need to re-create the save-set entry before you can restore it with ON–Bar. To re-create the save-set entry in the ISM catalog, execute ism_catalog -recreate_from from the command line. For details on how to recover expired save sets, see Re-Creating the ISM Catalog Before You Use ON-Bar and ism_catalog.
When a volume expires, ON–Bar can no longer restore any of the save sets. To recover an expired volume, execute ism_catalog -recover_from the command line. After you recover the volume, you can restore the save sets on this volume with ON–Bar.
The status of a save-set entry does not necessarily change to Expired on the same day that its retention period is exceeded. ISM changes the retention status for a save set when all the save sets that are dependent on it also exceed their retention periods. Save sets that contain level-1 and level-2 backups are dependent on the save set for the level-0 backup. This extra time ensures that an administrator can reconstruct a save set to a specific time in the retention period.
In Figure 6, the retention period is set for one week on the ISM server. The retention period for the save set for the level-0 backup that was performed on September 1 expires on September 8. The level-1 or level-2 backups that were performed during the rest of the week depend on this level-0 backup, so the entry for the level-0 backup does not expire until the entries for the level-1 and level-2 backups have also expired. During this time, you can use ON–Bar to restore the save sets.
On September 15, all the save sets from the backup cycle for the first week change status to Expired.
When the retention status of every save set on a volume has changed to Expired, ISM changes the recycling status of the volume to Eligible. Because a volume might contain many save sets, the recycling status of a volume might not change to Eligible for some time. All entries for Expired save sets remain listed in the ism_show -volume command until the volume is relabeled (either automatically or manually) or deleted from the ISM catalog. All the data on the volume remains available for recovery with the ism_catalog -recreate_from command until the volume is relabeled.
Therefore, the change in the recycling status of a volume to Eligible is a reminder to the administrator that the volume can be relabeled if conditions are right. If the administrator mounts the volume on a storage device with the Automatic Media Management option enabled, relabeling can occur automatically, and the existing data on the volume is no longer accessible to ISM. At this point, you can no longer recover the data on the storage volume.
When an administrator manually deletes a volume, the ISM server removes the entry for the volume from the ISM catalog. This action effectively releases the volume from the control of ISM. However, the data on a deleted volume is still available for recovery with the ism_catalog -recreate_from command. This command retrieves the information that is needed to re-create entries in the ISM catalog. Once entries are re-created in the ISM catalog, an administrator can use ON–Bar to recover the data. For details on recovering volumes that have been deleted from the ISM catalog, see Re-Creating the ISM Catalog Before You Use ON-Bar.
When a volume is automatically relabeled for reuse within the same pool, the volume name remains unchanged on the volume label. At this point, the volume is ready for new data. All original data is inaccessible and cannot be recovered. For more information on how ISM can automatically recycle storage volumes, see Relabeling Volumes Automatically.
Occasionally, you might want to keep data on a storage volume longer than the retention period that is specified for the ISM server. Changing the recycling status of a storage volume to Manual allows you to protect the volume from becoming eligible for automatic recycling. As long as the storage volume has a recycling status of Manual, ISM does not automatically recycle this volume, nor does it set the recycling status to Eligible. ISM continues to track the volume in the ISM catalog, and you can recover the data on the volume with the ism_catalog -recreate_from command. The storage volume is protected from automatic recycling until you remove the Manual recycling status or relabel the volume manually.
You can also use the Manual recycling status to create your own volume recycling policy. For example, suppose that you have a limited number of storage volumes and want to reuse them in a specific order, regardless of the age of the data on the volumes. You can apply the Manual recycling status to each volume and then relabel each volume as needed. The ISM server tracks these volumes in the ISM catalog until you relabel or delete them from the ISM catalog. For storage devices that have the Automatic Media Management option enabled, the volumes are protected from automatic recycling.
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