[gentoo-user] Re: [OT] Disappointing USB3 performance

[Grant Edwards]

On 2011-10-24, Florian Philipp <lists@×××××××××××.net> wrote:
> Am 24.10.2011 22:02, schrieb Grant Edwards:
>> On 2011-10-24, walt <w41ter@×××××.com> wrote:
>>
>>> I just bought an add-on USB3 adapter and outboard USB3/sata docking
>>> station, and I've been comparing the performance with my old e-sata
>>> outboard docking station.  Not so good :(
>>>
>>> After getting some unreliable results with hdparm, I settled on
>>> copying one 3GB file from one partition of the outboard drive to
>>> another partition of the same drive.  These results are highly
>>> reproducible, and favor e-sata over USB3 by a large margin.
>>>
>>> Over at least six trials on each docking station I consistently get
>>> 105 seconds for USB and 84 seconds for e-sata, a 5:4 ratio in favor
>>> of e-sata.
>>
>> Not surprising.  Did you expect that adding a gateway device to the
>> communication path and another protocol layer on top of SATA would
>> make things faster?
>>
>>> I used the same hard disk and the same pci-e slot in the same
>>> minimally-loaded machine for all the runs, and got very consistent
>>> results every time.
>>>
>>> Basically, the USB3/sata docking station gets the same throughput as
>>> the older sata 1 drives connected to the onboard pci sata controller,
>>> which is still pretty respectable for an outboard drive, I think.
>>
>> Yep, SATA performs the same as SATA. AFAIK, eSATA and SATA are
>> identical apart from the physical specs for the connector, a few minor
>> voltage level differences (to imporove noise tolerance), and hot-plug
>> support.
>
> Normal SATA also offers hotplug. Usually works, too.

I read somewhere that not all controllers support hotplug on
"internal" connectors, but I can't personally attest to having found
one that didn't.

>>> So, has anyone out there done similar tests on USB3 drives yet?
>>
>> There are disk drives that talk USB3 natively and aren't just using
>> USB<->SATA gateways?
>
> Well, there is USB Attached SCSI (CONFIG_USB_UAS in the kernel). It
> supports command queuing and works for USB-2.0 and 3.0 (but has
> additional software overhead for USB-2.0). I've not yet seen a
> compatible device, though.

Interesting.  Is USB3 peer to peer like SCSI and Firewire, or is it
the same master/slave poll/response scheme that has always crippled
USB?  Doing SCSI via a poll/response transport protocol seems like it
would lose most of the advantages of SCSI.

-- 
Grant Edwards               grant.b.edwards        Yow! He is the MELBA-BEING
                                  at               ... the ANGEL CAKE
                              gmail.com            ... XEROX him ... XEROX
                                                   him --