mac

bash-4.1# cat /proc/partitions
major minor  #blocks  name

   8        0  312571224 sda
   8        1   13895680 sda1
   8        2     102400 sda2
   8        3  123244191 sda3
   8        4          1 sda4
   8        5  165675008 sda5
   8        6    9650873 sda6
   8       16    7885824 sdb

bash-4.1# dd if=/dev/urandom of=00_rnd_init_data bs=1024 count=7885824
7885824+0 records in
7885824+0 records out
8075083776 bytes (8.1 GB) copied, 1510.37 s, 5.3 MB/s

bash-4.1# dd if=00_rnd_init_data of=/dev/sdb bs=1024 count=7885824
7885824+0 records in
7885824+0 records out
8075083776 bytes (8.1 GB) copied, 6328.48 s, 1.3 MB/s

bash-4.1# dd if=/dev/sdb of=01_rnd_read_data bs=1024 count=7885824
7885824+0 records in
7885824+0 records out
8075083776 bytes (8.1 GB) copied, 2866.41 s, 2.8 MB/s

bash-4.1# md5sum 0*rnd*
9550758eccefff8cbec9e5a3ff8e0b56  00_rnd_init_data
7095a52111cb66460cf8aaec21f350fb  01_rnd_read_data