ext4 and data consistency

That's a neat idea. I don't think we have cycle-accurate VMs in FOSS yet, but it doesn't matter for this, you can do the halt/check after every disk write, not every instruction. It still doesn't solve a major part of the problem -- you also need to exercise all the weird corner cases that only arise under certain sorts of memory pressure, or what happens if the disk is fragmented in *this* way and has *this* queue write depth and that makes the elevator algorithm tempted to reorder writes in an unfortunate way, etc. -- but it'd be really useful!