LACIEの外付けハードディスクを購入。中に入っているのが3.5インチHDで、USB3.0対応。

mac miniの内蔵のベンチが
Disk Test 57.07
Sequential 160.38
Uncached Write 192.89 118.43 MB/sec [4K blocks]
Uncached Write 170.24 96.32 MB/sec [256K blocks]
Uncached Read 113.07 33.09 MB/sec [4K blocks]
Uncached Read 198.51 99.77 MB/sec [256K blocks]
Random 34.71
Uncached Write 12.47 1.32 MB/sec [4K blocks]
Uncached Write 108.67 34.79 MB/sec [256K blocks]
Uncached Read 60.45 0.43 MB/sec [4K blocks]
Uncached Read 107.42 19.93 MB/sec [256K blocks]

そして、この外付けハードディスクが
Disk Test 66.83
Sequential 184.35
Uncached Write 312.58 191.92 MB/sec [4K blocks]
Uncached Write 281.11 159.05 MB/sec [256K blocks]
Uncached Read 82.92 24.27 MB/sec [4K blocks]
Uncached Read 347.08 174.44 MB/sec [256K blocks]
Random 40.81
Uncached Write 11.94 1.26 MB/sec [4K blocks]
Uncached Write 361.51 115.73 MB/sec [256K blocks]
Uncached Read 141.79 1.00 MB/sec [4K blocks]
Uncached Read 225.92 41.92 MB/sec [256K blocks]

と、内蔵よりも速い。内蔵のものが2.5インチHDだからであろう。