In addition to the overhead of software encryption, consider the effects
of the loss of hardware compression for the data written to tape, which
will affect both tape performance and thus elapsed time and the amount
of tape used. Both effects might pose challenges for jobs that need to
finish in a fixed amount of time or that were written to use a
particular number of tapes but might need more without compression.
This is overcome to some extent in some of the software encryption
products (including ours) by using hardware compression instructions to
compress the data before encrypting it. This of course uses more CPU
than simply encrypting and writing, but it avoids some of the problems
above.
However, note that the controller-based data compression algorithm, at
least for for IBM controllers (which, if I recall correctly, use a
modified ZL algorithm), provides better compression than that used by
the compression instructions (which I think might predate ZL), so there
might still be some breakage at the edges from performance and tape
utilization standpoints.
Last but not least, pay attention to key management in whatever solution
you choose. Security of storage, possibility of exposure, backup and
recovery, and DR are probably all things worth thinking about both from
operational and cost standpoints.
HTH...
O'Brien, David W. [C] , NIH/CIT wrote:
Can anyone suggest a methodology to measure GB per hour written to tape?
Management is seeking to evaluate the additional CPU overhead that s/w
encryption might entail.
IBM's Volume mount analyzer gives tape allocation and tape mounts per hour but
not, to my knowledge, GB written per hour.
Yes, we are still discussing h/w vs. s/w encryption. Thank you to all who
responded to the earlier thread.
Thank You,
Dave O'Brien
NIH Contractor
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John Eells
z/OS Technical Marketing
IBM Poughkeepsie
ee...@us.ibm.com
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