W dniu 16.04.2023 o 03:47, John Young pisze:
Although my post today is probably rhetorical question, I wanted to find out
whether this matters anymore or not.
Back in the late 2000's, IBM developed encryption facilities within the tape
drives, as this is also where compression was being performed. The idea was
that compression of data must occur before encryption, as encrypted data does
not compress well, and obviates the use of compression.
Nowadays, we've got pervasive encryption on z/OS. As a result, any data that
is backed up (for instance, ADRDSSU/FDR), is already encrypted.
Also, we now have zEDC, to compress data prior to storage, typically on disk.
To my question: With all the encryption and compression being performed on
disk, to what degree does TAPE COMPRESSION matter anymore?
Well, I would call it variety of choices.
Few remarks:
1. NO MORE TAPES connected directly to the z/OS. The last physical drive
TS1140 is out of support.
2. The above implies you use some VTS/VTL. IBM, EMC, Visara,
Secureagent, Luminex...
3. For IBM VTS you have several flavours of compression. One gives
better compression ratio, the other provide better throughput, etc.
4. Compressed data sent to VTS and compressed again yield "negative"
compression ratio, that means x:1, where x<1. This is not big increase,
BTW.
5. There is much richer variety of encryption types and flavours.
However I would bet not everyone encrypted every (possible) data on
DASD. Not to mention some encryption is completely transparent to tape
as the data is decrypted when sent to VTS CU. Example: FDE or FC end to
end.
6. Sometimes we encrypt already encrypted data. Example: encrypted
dataset sent over encrypted FICON to DASD with FDE (encrypted disk
modules). Sometimes it makes sense, sometimes it is redundant, but
really cheap (or free).
6. IMHO the most important: it is *our responsibility* to choose
features which are appropriate to given scenario.
My €0.02
--
Radoslaw Skorupka
Lodz, Poland
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