from: https://github.com/bitcoin/bitcoin/pull/12653/files
a1926362e -blocksdir: keep blockindex leveldb database in datadir
f38e4fdb0 QA: Add -blocksdir test
386a6b62a Allow to optional specify the directory for the blocks storage
also includes bugfix PR15124 (Ben Woosley)
ba8c8b2227 Fail if either disk space check fails