A bit late to the party, but I just tried #12653 and noticed some non-intuitive behavior (on macOS), that's probably worth explaining release notes and help.

Before this new feature I kept the entire datadir on an SSD drive, so I launch with: `bitcoind -datadir=/Volumes/SSD/Bitcoin`.

Initially I naively moved `/Volumes/SSD/Bitcoin/blocks` to `/Users/bitcoin/blocks` and added a line to `/Volumes/SSD/Bitcoin/bitcoin.conf`: `blocksdir=/Users/bitcoin/blocks`.

I then realized that I shouldn't have moved the `index` subdirectory, so I moved that back to `/Volumes/SSD/Bitcoin/blocks/index`. Having an empty `blocks` dir with just and `index` subdir is a bit weird. Perhaps after @jimpo's #11857 is merged, we could just move / assume all indexes to be there (if `-blocksdir` is set)?

Worse, it created a directory `/Users/bitcoin/blocks/blocks`, which seems like a bug. I had to set `blocksdir=/Users/bitcoin` instead.
#include <sys/stat.h>
#endif
#include <boost/algorithm/string/classification.hpp>
#include <boost/algorithm/string/replace.hpp>
#include <boost/algorithm/string/split.hpp>
#include <boost/bind.hpp>
#include <boost/thread.hpp>
#include <openssl/crypto.h>
#if ENABLE_ZMQ
#include <zmq/zmqnotificationinterface.h>
#include <zmq/zmqrpc.h>
#endif
bool fFeeEstimatesInitialized = false;
static const bool DEFAULT_PROXYRANDOMIZE = true;
static const bool DEFAULT_REST_ENABLE = false;
static const bool DEFAULT_STOPAFTERBLOCKIMPORT = false;
std::unique_ptr<CConnman> g_connman;
std::unique_ptr<PeerLogicValidation> peerLogic;
#ifdef WIN32
#define MIN_CORE_FILEDESCRIPTORS 0
#else
#define MIN_CORE_FILEDESCRIPTORS 150
#endif
static const char* FEE_ESTIMATES_FILENAME="fee_estimates.dat";
/**
 * This is a minimally invasive approach to shutdown on LevelDB read errors from the
 * chainstate, while keeping user interface out of the common library, which is shared
 * between bitcoind, and bitcoin-qt and non-server tools.
*/
class CCoinsViewErrorCatcher final : public CCoinsViewBacked