Planning for virtual tape storage

To prepare to use virtual tape storage, you need to consider these items:

• Whether you have the authority to create virtual images
• How much disk space you have

  Because virtual images are stored on your disk units, they can quickly use disk space. It is essential that you determine whether you have enough disk space. The smallest allowable size for a tape image file volume is 48 MB. The largest allowable size is 1000000 MB.

  To determine how much disk space you have, follow these steps:

  1. From IBM® Navigator for i, expand Configuration and Service > Disk Pools.
  2. Right-click the Disk Pool you want to view, and select Properties.
  3. Select the Capacity tab. The Capacity page displays the used space, free space, total capacity, threshold, and percentage of disk space used for the disk pool.
  Note: The default value of the Catalog ASP threshold is set to *CALC. This value sets the maximum allowed storage threshold for virtual tape to be the greater of 95% or 5 GB of free space remaining in the ASP. The tape operation stops with an end of media error when the maximum allowed storage threshold for virtual tape is reached.
  You can also use the Work with Disk Status (WRKDSKSTS) command to determine your free space. If you need to free up disk space, follow these steps:

  1. Remove any unused virtual tape volumes by using Remove Image Catalog Entry (RMVIMGCLGE) KEEP(*NO).
  2. Free up any unused space within an existing virtual tape volume by using Change Image Catalog Entry (CHGIMGCLGE) Allocate Storage (ALCSTG)(*MIN), or free up any unused space within all of the virtual tape volumes within an image catalog by using CHGIMGCLG ALCSTG(*MIN).
  3. Delete any unused objects.
  4. Save objects by specifying STG(*FREE).
  5. Save the old log versions of QHST that are not currently used and then delete them.
  6. Print or delete spooled files on the system.
• The number of virtual images volumes you need
  To determine how many volumes you need, follow these steps:

  1. Determine how much data you plan to store.
  2. Determine the size of each virtual image. Determine image size based on what you plan to do with the tape image file. Keep files small if you want to electronically transfer them to another system.
• The maximum block size supported by the physical tape device that the virtual tape volume will be saved to
• That the user profile that is used to create the virtual tape volumes has its maximum storage allowed attribute set to *NOMAX