Intermittent pauses copying from one usb drive to another

Hans Petter Selasky hselasky at
Sat Feb 5 14:34:58 UTC 2011

On Saturday 05 February 2011 14:27:56 Donald Allen wrote:
> I've discussed problems with FreeBSD and usb sata drives on this list
> in the past (as recently as last September), and have given up on
> FreeBSD as a result of the usb disk problems (I do my backups with usb
> drives) and other usb-related issues. But I've now replaced the usb
> enclosures I was using at that time and have acquired some Toshiba usb
> drives, so with this new equipment, I thought I'd give FreeBSD another
> try, since generally I prefer it to Linux. But I'm having problems
> again.
> Plugging in the Toshiba drives produces entries like this in
> /var/log/message:


Errors happen because the USB firmware of your USB hardware does not support 
all the SCSI commands issued by the CAM/SCSI layer. This is a well known 
problem. Probably Linux is better at filtering the SCSI commands passed to the 
various devices.

Proof: I have a custom USB test software suite actually running under FreeBSD 
which can stress test mass storage devices. So far very few USB mass storage 
devices I've seen pass all the tests and recover properly. Most disks/memory 
sticks simply die at the first non-supported SCSI command and/or error 
scenario even though the SCSI and USB mass storage wrapper for SCSI commands 
define error codes to be returned in case of failure. Contact me off-list if 
you are interested in this.

Solution: USB mass storage devices needs to be crippled down to a few SCSI 
commands like READ_12 and WRITE_12. This is not a USB problem. It needs to be 
done in the CAM/SCSI layer.

What you can do: Ask the vendor to test their USB devices with FreeBSD 8.2 
before shipping.


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