On Tue, 30 Sep 2014 14:10:28 +0800 "Lu, Baolu" <baolu.lu@xxxxxxxxxxxxxxx> wrote: > I tried to reproduce this issue. I connected a USB key under a > full-speed hub. > > sg_rbuf returns error which I am not familiar with. > > allen@allen-ivb:~$ lsusb -t > [...snip...] > /: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/3p, 480M > |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M > |__ Port 4: Dev 11, If 0, Class=Hub, Driver=hub/3p, 12M > |__ Port 1: Dev 12, If 0, Class=Human Interface Device, > Driver=usbhid, 12M > |__ Port 1: Dev 12, If 1, Class=Human Interface Device, > Driver=usbhid, 12M > |__ Port 3: Dev 15, If 0, Class=Mass Storage, > Driver=usb-storage, 12M > > allen@allen-ivb:~$ sudo dd if=/dev/zero of=/dev/sdb bs=4k count=1k > 1024+0 records in > 1024+0 records out > 4194304 bytes (4.2 MB) copied, 4.32676 s, 969 kB/s > > allen@allen-ivb:~$ sudo sg_rbuf --buffer=524288 -q -t -v /dev/sg2 > Read buffer cdb: 3c 03 00 00 00 00 00 00 04 00 > READ BUFFER descriptor error: SCSI status: Check Condition > Fixed format, current; Sense key: Illegal Request > Additional sense: Invalid command operation code You won't be able to use sg_rbuf. sg_rbuf issues READ BUFFER commands, which most/all USB sticks won't support. Using dd instead should be fine to show the problem. In the USB tree you posted, the hub is connected to a USB 2.0 port and the 969KB/sec dd result looks reasonable. Now try with the USB 1.1 hub connected to a USB 3.0 port. For my testing, I increased the maximum USB transfer size using a command like echo 1024 >/sys/block/sdb/device/max_sectors [By default the kernel limits transfers to 120KB (240 512-byte sectors), presumably because some devices break with larger ones. Changing that shouldn't be necessary to show the problem though.] If you want to bypass the block layer, you could use ddpt instead of dd; see http://sg.danny.cz/sg/ddpt.html ddpt can issue SCSI commands directly, so you could do something like ddpt if=/dev/sdb of=/dev/null bs=512 bpt=240 count=65536 verbose=2 iflag=pt to time reading the first 32MB. Mark -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
