Just how fast is USB 3.0?

USB 3.0 isn’t exactly new, and everyone knows how fast it is compared to USB 2.0.  I bought my first USB 3.0 device yesterday — an external hard disk — and I was curious how fast it really was.  I used hdparm as described in an Ask Ubuntu answer to compare the speeds of 3 different storage devices I had.

Fastest was, unsurprisingly, the internal mSATA SSD my laptop had, at about 180MBps.  The new USB 3.0 hard disk (a Western Digital one) managed to read data at 105MBps.  This number is very impressive when juxtaposed next to my old USB 2.0 drive (a Hitachi) which could read only at around 34MBps.

Raw numbers for the curious and for posterity:

% sudo hdparm -Tt /dev/sda    # Internal SSD
/dev/sda:
 Timing cached reads:   8624 MB in  2.00 seconds = 4314.43 MB/sec
 Timing buffered disk reads: 544 MB in  3.02 seconds = 179.89 MB/sec

% sudo hdparm -Tt /dev/sdb    # USB 3.0 external HDD
/dev/sdb:
 Timing cached reads:   8584 MB in  2.00 seconds = 4293.72 MB/sec
 Timing buffered disk reads: 318 MB in  3.01 seconds = 105.54 MB/sec

% sudo hdparm -Tt /dev/sdb    # USB 2.0 external HDD
/dev/sdb:
 Timing cached reads:   8434 MB in  2.00 seconds = 4219.40 MB/sec
 Timing buffered disk reads: 102 MB in  3.03 seconds =  33.69 MB/sec