Sock Sock Shoe Shoe
A client complained that their tape drives were not compressing data as well as it used to. Investigating further reminded me of a scene from the 1970's television show "All in the family", summarized well inAmerican Scientist:
... in one episode of All in the Family, Archie Bunker's son-in-law, Mike, watches Archie put on his shoes and socks. Mike goes into a conniption when Archie puts the sock and shoe completely on one foot first, tying a bow to complete the action, while the other foot remains bare. To Mike, if I remember correctly, the right way to put on shoes and socks is first to put a sock on each foot and only then put the shoes on over them, and only in the same order as the socks. In an ironic development in his character, the politically liberal Mike shows himself to be intolerant of differences in how people do common little things, unaccepting of the fact that there is more than one way to skin a cat or put on one's shoes.
Both agreed that socks go first, then shoes, but the actual deployment was different.
In the case of this customer, a recent change was the use of "encryption" before the data reached the tape drive. In regards to compression and encryption, you should always compress first, then encrypt. Compression algorithms rely on frequency of data, for example the letter "E" appears more often in the English language than the letter "Z". However, once you encrypt data, those data patterns are randomized, and any attempt to compress the data afterwards is wasted effort.
With IBM tape encryption on either the TS1120 or LTO4 tape drives, we compress, then encrypt, the data when it arrives to the tape drive, so that the compression has some chance of getting up to 3:1 reduction. This comp So, just as the case between Archie Bunker and his son-in-law, there are many ways to deploy compression and encryption, just make sure you do them in the right order to get the most benefit.
So, just as the case between Archie Bunker and his son-in-law, there are many ways to deploy compression and encryption, just make sure you do them in the right order to get the most benefit.