Re: [gentoo-user] Re: [OT] Disappointing USB3 performance
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. 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. Regards, Florian Philipp signature.asc Description: OpenPGP digital signature
Re: [gentoo-user] Re: [OT] Disappointing USB3 performance
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.
Re: [gentoo-user] Re: [OT] Disappointing USB3 performance
On Oct 24, 2011 7:21 PM, walt w41...@gmail.com wrote: On 10/24/2011 10:28 AM, walt wrote: ... 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/sata over USB3/sata... Wow, lots of great answers, guys, thanks. Enough material to give me lots more questions to ask you :) Like, for example, in theory the raw bit-rate for USB3 is more than enough to keep up with any existing consumer hard drive, right? The speed of usb/sata protocol translation should be very fast compared to the speed of a spinning mechanical disk (I think?) Now, lack of DMA is another story for hard disks, certainly. Here's where my ignorance of hardware limits my thinking: AFAIK the device driver *always* sits between the disk drive and the DMA hardware, doesn't it? DMA means a device is told where in the system's address space it may write to, and it writes directly to that place without further CPU involvement. Since drivers run on the CPU, the drivr isn't a go-between. When the CPU *is* involved in the passing of bits around, things slow down. IIRC, that's called PIO--programmed IO.
Re: [gentoo-user] Re: [OT] Disappointing USB3 performance
On Mon, Oct 24 2011, Michael Mol wrote: On Oct 24, 2011 7:21 PM, walt w41...@gmail.com wrote: Now, lack of DMA is another story for hard disks, certainly. Here's where my ignorance of hardware limits my thinking: AFAIK the device driver *always* sits between the disk drive and the DMA hardware, doesn't it? DMA means a device is told where in the system's address space it may write to, and it writes directly to that place without further CPU involvement. Since drivers run on the CPU, the drivr isn't a go-between. When the CPU *is* involved in the passing of bits around, things slow down. IIRC, that's called PIO--programmed IO. Correct. DMA stands for direct memory access; the device has direct access to the memory. PIO is indeed the name when the CPU acts as a go between. allan
Re: [gentoo-user] Re: [OT] Disappointing USB3 performance
USB does use DMA. Check the kernel source doco Documentation/usb/dma.txt
