OK, but what stops them from daily performing a mirror clone, checking it for consistency, then backing that up? As mentioned in the linked update, 30 complete backups would consume only 900GB, so you could keep weeks of daily backups, plus weekly and/or monthlies going back much further, for a terabyte of space. That way, in the worst case, you could go back to a backup before the corruption began. Obviously you would want to have plenty of safeguards in place so that that never happened, but just in case, it's good to have an honest to goodness backup too.