Thank you so much for these kind ideas.

     If you want to save more space, you have to hack
     the different BTC forks to refer back to the BTC
     chain for the parts in common prior to the forks.
     Buying disk is easier.

   hadn't thought of the source mutation (nor did I know zfs had zstd).
   you can use hardlinks to deduplicate the block files, too.  takes some
   carefulness.
   note to self: disks with dedicated purposes might be simpler for me

     > 1930 a hard thing that's remaining is software to archive files on
     > bitcoinsv.
     You should be able to scan through all tx writing each
     attachment into a filename <txid>-<content_hash>