>> > I'm testing this USB 3.0 bus-powered hard drive: >> > >> > http://www.amazon.com/gp/product/B0041OSQ9S >> > >> > and I get: >> > >> > # hdparm -tT /dev/sdb >> > /dev/sdb: >> > Timing cached reads: 8006 MB in 2.00 seconds = 4004.33 MB/sec >> > Timing buffered disk reads: 252 MB in 3.01 seconds = 83.63 MB/sec >> > >> > # hdparm -tT /dev/sdb >> > /dev/sdb: >> > Timing cached reads: 8230 MB in 2.00 seconds = 4116.54 MB/sec >> > Timing buffered disk reads: 252 MB in 3.02 seconds = 83.55 MB/sec >> > >> > # hdparm -tT /dev/sdb >> > /dev/sdb: >> > Timing cached reads: 8446 MB in 2.00 seconds = 4224.36 MB/sec >> > Timing buffered disk reads: 230 MB in 3.02 seconds = 76.28 MB/sec >> > >> > Wikipedia says USB 3.0 has transmission speeds of up to 5 Gbit/s. >> > Doesn't MB/sec denote mega*bytes* per second? >> > >> > - Grant >> >> 4000MB/s = 4Gb/s > > > please read man hdparm > > -T Perform timings of cache reads for benchmark and comparison purposes. > For meaningful results, this operation > should be repeated 2-3 times on an otherwise inactive system (no > other active processes) with at least a couple > of megabytes of free memory. This displays the speed of reading > directly from the Linux buffer cache without > disk access. This measurement is essentially an indication of > the throughput of the processor, cache, and mem- > ory of the system under test. > > > as you can see, those numbers have nothing to do with the transport. > > And 80mb/sec for a harddisk is really, really good.
Here's what I get from the same hard drive plugged into a USB 2.0 port: # hdparm -t /dev/sdb /dev/sdb: Timing buffered disk reads: 102 MB in 3.01 seconds = 33.90 MB/sec # hdparm -t /dev/sdb /dev/sdb: Timing buffered disk reads: 92 MB in 3.00 seconds = 30.66 MB/sec # hdparm -t /dev/sdb /dev/sdb: Timing buffered disk reads: 102 MB in 3.03 seconds = 33.63 MB/sec So USB 2.0 throughput is obviously creating a bottleneck. USB 2.0 throughput is said to be 60 MB/s so I'm surprised I'm not doing much better than 30 MB/s there. USB 3.0 throughput is said to be 625 MB/s so I must be running up against the speed of the disk itself in USB 3.0 mode, correct? Here's what I get from my internal SATA hard drive, but it is surely a much faster disk: # hdparm -t /dev/sda /dev/sda: Timing buffered disk reads: 412 MB in 3.01 seconds = 136.99 MB/sec # hdparm -t /dev/sda /dev/sda: Timing buffered disk reads: 412 MB in 3.01 seconds = 136.75 MB/sec # hdparm -t /dev/sda /dev/sda: Timing buffered disk reads: 414 MB in 3.01 seconds = 137.55 MB/sec - Grant
