ISM uses volume labels to track your data. Relabeling a volume means that you can no longer recover the original data on the volume. To relabel a volume, use the ism_op -label command. You can relabel a volume only if it is unmounted. If you delete a volume from the ISM catalog, It is recommended that you do not use the deleted volume name for a new volume unless you are sure that you will never need to recover the data on the original volume.
You can relabel a volume whenever you want to. But to ensure that your data is protected, we recommend that you relabel a volume only under the following conditions:
When the retention periods for all the save sets on a volume expire and their retention status is marked Expired, the recycling status of the storage volume changes to Eligible. At this point, you know that the retention period set for the ISM server for all the data on the volume has expired. If you use the Automatic Media Management option, ISM automatically relabels the volume and overwrites it 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 volume with a lower label number. ISM labels recycled volumes in this way so that you can easily determine the age of your volumes. Each time that a volume is relabeled, it receives a new two-year expiration date. Lower-numbered volumes typically are older than higher-numbered volumes, even though the data on the older volume might be more recent.
Eligible volumes are recycled within the same pool. For example, an eligible volume from the ISMData pool remains in the ISMData pool when it is relabeled. If you want to recycle a volume to a different pool, you must manually label the volume and change the volume pool selection. For more information, see Recycling a Volume or Adding More Volumes to a Pool.
You can manually relabel a storage volume at any time. If you relabel a storage volume before it is eligible for recycling, the retention period for some of the save sets on the volume have not yet expired, and you risk losing valuable data. Once a storage volume is relabeled, you can no longer recover the original data.
If you use a file-type device, you need to relabel the file-type volume mounted on the file-type device when the volume fills with data. ISM tracks file-type volumes in the same way that it tracks other volumes. If you relabel the file-type volume, you can no longer recover the original data. To ensure that the data is protected, we recommend that you clone the data on your file-type volume to tape before you relabel the volume. ISM tracks cloned volumes in the same way that it tracks source volumes. When you clone your data to tape before you relabel a file-type volume, you ensure that you can recover the data.
After the file-type volume is relabeled, it appears to the ISM server that a new file-type volume is available to be mounted.
For more information on cloning volumes, see Cloning Storage Volumes.
Both recycling eligible volumes and adding more volumes to a pool have advantages. When you recycle, you reuse the same volumes and do not add new volumes to the pool. However, the media might wear out over time and have a higher failure rate. ISM uses the original volume sequence number to relabel volumes within the same volume pool. This number enables you to easily track which volumes are older. When you relabel a volume to a different volume pool, the volume receives the next available sequence number for the new pool. Because each volume receives a new two-year expiration date when it is relabeled, you cannot determine how old a specific volume is when it is relabeled to a different volume pool.
On the other hand, if your site requires you to maintain the backups in storage for a certain period of time, you might have to add more media to the volume pool instead of recycling it. For example, if your volumes fill up in 90 days but your retention period is set for 180 days, you need to add new media to the pool until you can recycle the backup volumes that contain expired or old backups.
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