--- variant 1: block_size=0 -- the CAM layer filters this at
    cam_xpt.c:3063-3071 (heads=0, CAM_REQ_CMP, NO trap):
[calcgeom] survived: heads=0 spt=0 cyl=0 status=0x1
--- variant 2: block_size=2MiB (>1MiB): filter passes, production
    btaction computes (1024*1024)/block_size == 0 then divides
    volume_size by it (bt.c:1157-1158) -> #DE -> kernel panic: