Administrator's Guide

How ADSM Uses and Reuses Removable Media

ADSM helps you to manage removable media by providing ways to control how removable media are used and reused. The following describes a typical life cycle for a piece of media. The numbers (such as (1)) refer to numbers in Figure 9.

1. You label (1) and check in (2) the media.

2. If you choose not to use scratch volumes in the storage pool associated with the device, you define the volumes. However, use of scratch volumes is more convenient in most cases.

   Figure 9. Simplified View of the Life Cycle of a Tape
   
   
   
   

3. A client sends data to the server for backup, archive, or space management. The server stores the client data on the volume. Which volume the server selects (3) depends on:

   • The policy domain to which the client is assigned.

   • The management class for the data (either the default management class for the policy set, or the class specified by the client in the client's include/exclude list or file).

   • The storage pool specified as the destination in either the management class (for space-managed data) or copy group (for backup or archive data). The storage pool is associated with a device class, which determines which device and which type of media is used.

   • Whether the MAXSCRATCH value is reached when the scratch volumes are selected.

   • Whether collocation is enabled for that storage pool. When collocation is enabled, ADSM attempts to place data for different clients or client nodes on separate volumes.

   See Figure 10.

   Figure 10. How ADSM Affects Media Use
   
   
   
   

4. The contents of the volume change over time as a result of:

   • Expiration of files (4) (affected by management class and copy group attributes, and the frequency of expiration processing)

   • Movement and deletion of file spaces (by an ADSM administrator)

   • Automatic reclamation of media by ADSM (5)

     The amount of data on the volume and the reclamation threshold set for the storage pool affects when the volume is reclaimed. When the volume is reclaimed, any valid, unexpired data is moved to other volumes or possibly to another storage pool (for storage pools with single-drive libraries).

   If the volume becomes empty because all valid data either expires or is moved to another volume, the volume is available for reuse (after any time delay specified by the REUSEDELAY parameter for the storage pool). The empty volume becomes a scratch volume if it was initially a scratch volume. The volume starts again at step 3.

5. You determine when the media has reached its end of life.

   For volumes that you defined (private volumes), check the statistics on the volumes by using the QUERY VOLUME command. The statistics include the number of write passes on a volume (compare with the number of write passes recommended by the manufacturer) and the number of errors on the volume.

   You must move any valid data off a volume that has reached end of life. Then, if the volume is in an automated library, check out the volume from the library. If the volume is not a scratch volume, delete the volume from the ADSM database.