On Mon, Oct 24, 2011 at 4:31 PM, Grant Edwards <grant.b.edwa...@gmail.com> wrote: > On 2011-10-24, Florian Philipp <li...@binarywings.net> wrote: >> Am 24.10.2011 22:02, schrieb Grant Edwards: >>> On 2011-10-24, walt <w41...@gmail.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.
IIRC USB3 is interrupt-driven instead of constantly polling the device.
