Relabeling Volumes Automatically

If ISM detects a storage volume from the appropriate pool with the Recycle status of Eligible, ISM mounts, relabels, and overwrites the storage volume with new data. However, the new label uses the same name and sequence number as the original label. Therefore, newer data might be on a storage volume with a lower label number. ISM labels recycled storage volumes in this way to provide you with an easy way to determine the age of your storage volumes. Lower-numbered storage volumes typically are older than higher-numbered storage volumes, even though the data on the older storage volume might be more recent.

For example, suppose that over time you add ten storage volumes, ISMData.0001 through ISMData.0010, to the ISMData volume pool. When the retention periods for all the save sets on ISMData.0001 expire, ISMData.0001 becomes eligible for automatic recycling. During a backup operation, the ISM server searches for a writable storage volume from the ISMData volume pool. If ISMData.0001 is the only volume from the ISMData pool loaded in a storage device, or if the ISM server needs more than one volume to complete the backup operation and no other writable volumes from the ISMData pool are detected, the ISM server automatically relabels and mounts ISMData.0001 and continues the backup operation. ISM relabels ISMData.0001 with the same name and sequence number. However, the original data on ISMData.0001 can no longer be recovered.

Although the data on ISMData.0001 might be more recent than the data on ISMData.0010, you can tell at a glance that the physical media on ISMData.0001 is older than ISMData.0010. Because storage media can wear out over time, this labeling scheme enables you to monitor the age of your media.

ISM gives each physical volume a default expiration date of two years after it is labeled. If you relabel a volume, it gets a new two-year expiration date. The expiration date of a storage volume refers to the physical media, not the data on the volume. When a volume reaches its expiration date, ISM automatically changes the Backup status of the volume to Disabled. This status means that no new data can be written to the volume. However, the data on the volume can still be recovered until the volume is relabeled.

To determine the expiration date of your physical media, execute the ism_show -volumes command at the command line. If you relabel volumes within the same volume pool, however, you can easily determine the relative age of a volume by the volume sequence number.