Re: [gentoo-user] {OT} USB 3.0 hard drive speed test

[Grant <emailgrant@gmail.com>]

>> > 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