>can anybody tell how much data (mb) you are writing on a tape (IBM3590-E or
>STK9840) when using HW-Compression and TSM-Client-Compression together.
Winfried - The conceptually simple answer is that no tape can hold any
more bytes than its rated capacity per recording format.
For example, the base 3590 tape with base drives is rated for 10 billion
bytes. There is no way you can get more than 10 billion physical bytes
recorded on it. Compression simply causes original data to be
re-represented so as reduce demands upon that physical capacity such that
you can push more data out to it.
As to the specifics of what you want to do, which is to gauge
compression effectiveness: You have to gather numbers at each
"compression gate". First collect the byte count sent by the client.
Then, on the server, when the tape volume becomes Full, you can find
how many bytes the server has written to the tape drive. (Remember
that the server is blissfully ignorant of how the tape drive is
actually dealing with the data as writing proceeds such that only
when the tape drive can take no more for that volume does it become
apparent what the drive compression result is.)
There would be less uncertainty in this whole area if IBM would
publish information about compression in their client and drives.
Thus far, the respective manuals contain scant information and no
references. (I've been prompting the software and hardware
documentation folks to improve this area.)
Richard Sims, BU
