%diskinfo -c /dev/gvinum/media
/dev/gvinum/media
        512             # sectorsize
        80027320320     # mediasize in bytes (75G)
        156303360       # mediasize in sectors

I/O command overhead:
        time to read 10MB block      0.395564 sec       =    0.019 msec/sector
        time to read 20480 sectors   3.189842 sec       =    0.156 msec/sector
        calculated command overhead                     =    0.136 msec/sector

%diskinfo -c /dev/ad0
/dev/ad0
        512             # sectorsize
        20020396032     # mediasize in bytes (19G)
        39102336        # mediasize in sectors
        38792           # Cylinders according to firmware.
        16              # Heads according to firmware.
        63              # Sectors according to firmware.

I/O command overhead:
        time to read 10MB block      0.456698 sec       =    0.022 msec/sector
        time to read 20480 sectors   2.727879 sec       =    0.133 msec/sector
        calculated command overhead                     =    0.111 msec/sector