21Gb is huge - For first time download, with people capped internet at 20Gb per month. {Most 3rd world countries, still use capped internet}
Can it not be commpressed daily {Zip / Rar etc} and be placed on a fast P2P site? {auto proccess} As a backup?
Rather than having to download the whole thing?
Probably not. Compression only works on files that have lots of redundancy. For example, source code files (C, Python, etc) have lots of redundancy because some symbols are more common than others. Executable files have less redundancy and cannot be compressed as well. To be effective, bitcoin dat files should have low redundancy. Encryption techniques also reduce redundancy in files because redundancy provides clues to an attacker.
The real solution might be to find some way to collapse the older transactions into some sort of archive so we newbes don't have to down load more than a couple of years to be productive. If the archives were distributed over the internet they would be available everywhere as needed.
Nope, the solution is to read first. If you want to mine you dont need a full node. Just take mining software like cgminer and connect to a mining pool. Are you trying to soloming with a GPU here?
If you just want a wallet, take one of the light wallets, e.g. electrum or multibit.
If its a problem for you to download the blockchain, dont. There is no need unless you want to support the network or solo mine