Just by the by, this is a terrible idea to do online. The best case is a crash-consistent replica. The more likely case is an inconsistent one that may or ma

Just by the by, this is a terrible idea to do online. The best case is a crash-consistent replica. The more likely case is an inconsistent one that may or may not be repairable, because of the length of time it takes to do the dump. If you want a bit-for-bit dump of an online filesystem, use Linux LVM to create a snapshot, then make an image of that (100% known crash-consistent) copy.