Formatting of virtual tape images

The density (format) parameter limits the block size that can be written to a virtual tape volume so that the volume is compatible for duplication to your physical tape device.

  • Volumes with a density of *VRT256K use an optimum and maximum block size of 256 KB.
  • Volumes with a density of *VRT240K use an optimum and maximum block size of 240 KB.
  • Volumes with a density of *VRT64K use an optimum and maximum block size of 64 KB.
  • Volumes with a density of *VRT32K do not use an optimum and maximum block size and are compatible with all devices.
Note: The application using the tape device controls the actual block size used when data is written to a virtual tape volume. An application can write data blocks to virtual tape volumes that are smaller than the maximum block size.

You cannot copy your virtual tape media to physical media if you choose an incompatible block size. Ensure that you pick a virtual tape density with a block size that is compatible with the physical tape devices on your system by performing one of the following:

  • For tape library devices in IBM® Navigator for i, expand Configuration and Service > All Tasks > Tape Devices > Tape Libraries > Tape Resources. Next, right-click the device that you want to view and select Properties to display the supported block sizes for your tape device.
  • For stand-alone tape devices in IBM Navigator for i, expand Configuration and Service > All Tasks > Tape Devices > Stand-Alone Devices . Next, right-click the device that you want to view and select Properties to display the supported block sizes for your tape device.
  • Save a small library to your physical tape drive with the USEOPTBLK parameter set to *YES. Type DSPTAP DATA(*LABELS) on a command line, and see the Block Length field for the block size that was used.
Note: The Initialize Tape (INZTAP) command makes any pre-existing data on the virtual tape volume inaccessible by the virtual tape device. The INZTAP command with the parameter CLEAR(*YES) can be used to delete any existing data in a virtual tape volume, but this should only be used if you have security concerns with the existing data because this operation can take a long time and uses significant system resources.