-b block-size
              Specify  the  size  of  blocks in bytes.  Valid block-size values are 1024, 2048 and 4096 bytes per
              block.  If omitted, block-size is heuristically determined by the filesystem size and the  expected
              usage  of  the  filesystem  (see  the  -T option).  If block-size is negative, then mke2fs will use
              heuristics to determine the appropriate block size, with the constraint that the block size will be
              at  least  block-size  bytes.   This  is useful for certain hardware devices which require that the
              blocksize be a multiple of 2k.