z/OS DFSMS Implementing System-Managed Storage
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Using the Virtual Tape Server (VTS) to Optimize Tape Media

z/OS DFSMS Implementing System-Managed Storage

Another method for optimizing your tape media is through the Virtual Tape Server (VTS) tape library hardware. You can use VTS with or without tape mount management. It does not require ACS routine or other software changes.

VTS lets you define up to 32 virtual tape drives to the host. Not visible to the host are up to 6 physical tape devices. When the host writes to one of the virtual devices, it actually writes to a virtual volume residing on the VTS DASD buffer. The VTS, transparent to the host, copies the entire virtual volume onto a logical volume that is then mapped to physical stacked volumes known only to the VTS.

These logical and physical volumes cannot be ejected directly. However, VTS offers many other advantages. For example, VTS:
  • Does not need a DASD buffer
  • Does not use DFSMShsm facilities to fully stack tapes
  • Does not require double data movement in the host
  • Does not require changes to ACS routines
  • Fully uses tape media due to the structure of the virtual volumes on the physical tape

VTS avoids the extensive analysis required to use tape mount management. You can, however, use VMA studies to use VTS more effectively, since these studies identify useful information, such as data sets needing to be stored offsite, or temporary data sets that can be written to DASD and expired.

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