On Thu, Aug 11, 2011 at 1:50 PM, Grant <emailgr...@gmail.com> wrote: >>> > 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?
Those speeds seem good and normal to me, much faster than USB 2.0 would have provided. And really good for a low-power drive. Faster than my USB 3.0 32GB flash drive. :) Here's a benchmark of 2.5" USB 3.0 external drives, in fact yours is one of the tested disks. Your speeds above are actually faster than the benchmarked speeds: http://www.everythingusb.com/images/list/portable-drive-large-file-copy-benchmark.png > 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 2.0 theoretical max is 480Mbps but realistically it is more like 320Mbps, which means your speeds above are just about as fast as anyone is ever going to get on USB 2.0, and they are in line with the fastest speeds I've ever gotten personally on USB 2.0. Roughly about 32 MB/sec is "maximum speed" on USB 2.0 in my experience. > 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? Processing power of the external USB<->SATA controller chip could also come into play. But in your case I think you're getting the maximum speed possible from the drive. Be happy. :) >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 Surely a faster/higher-powered disk and I would guess that USB 3 maybe has higher latency than the SATA controller on your laptop's motherboard. I know USB 2.0 has latency problems (and why the audio nerds* prefer firewire equipment). * used as a term of endearment :)
