HSM in a Virtual Tape Environment - Part 1

To have HSM create its (his? her?) backups, migates and dumps in a virtual tape enviroment some issues regarding tape recycling have to be addressed.

Because tape is virtual, the old-skool need for recycle (free up tapes!) is no longer as valid as it was, as the amount of tapes is a multitude of the amount one had in a physical environment. Virtual tapes however are not limitless, and one should keep the amount of tapes HSM 'manages' in repectable quantities.

Major drawbacks on the HSM recycle in a virtual environment is the immense negative impact this 'housekeeping-task' has on the cache on the virtual tape environment. This is even a bigger issue when one has more than only HSM as an exploiter of the VTS.

Ideally one would want to only recycle the empty tapes (percentvalid = 0). In order to get some isight in the the 'príce' one has to pay for this (via a higher tape consumtion by HSM) one should look at the following figures:

• number of tapes being used from the scratch pool each day
• how many of these are HSM
  
• life cycle for your non-hsm tape data
  
• life cycle for your hsm data (mostly dependent on life-cycle for original data)
  (some parameters influencing this are RETAINDAYS ONLY BACKUP, RETAINDAYS EXTRA BACKUPS, PRIMARY DAYS, LEVEL 1 DAYS)
• number of tapes being freed by (daily/weekly?) recycle tasks
• Valid Data Distribution on HSM datasets (pctvalid from LIST TTOC) (=trigger for recycle)
  
• Valid Data Distribution on HSM tapes (this is *not* pctvalid from TTOC) a tricky value in a VTS environment
  

The nest part of this post will address how all these values will provide the information needed to tweak HSM (and maybe even the VTS) to reduce the negative impact of HSM in a VTS as much as possible.