Re: System hangs when using USB 3.0 HD with on Ubuntu

Alan Stern
2010-04-02T14:57:31Z

On Fri, 2 Apr 2010, James Bottomley wrote:

> > > Does the command sent by hdparm look familiar? Exactly, it is the
> > > third ATA command (IDENTIFY DEVICE) we discovered earlier and caused
> > > the drive to stall.
> >
> > That's nice to know. Other people have been reporting similar
> > problems. Now we can tell where they come from.
>
> Yes ... I think we're starting to need to get a handle on all these
> userspace random pokes which can disrupt (the admittedly badly written
> and badly tested) devices which the kernel tries so hard not to upset.
>
> > > Does anyone know why the drive would not be able to cope with this
> > > command?
> >
> > No idea. Except that it's probably not the drive's fault, but rather
> > the fault of the USB-(S)ATA chip that controls the drive.
>
> Best guess (and it's a guess only) would be that the USB bridge SAT
> layer doesn't implement ATA_16 and so fails in interesting ways when it
> comes in. Does the ATA_12 version of IDENTIFY DEVICE succeed?

It does. And in between the two is an ATA_16 SET FEATURES command
which also (apparently) succeeds. That is, there is no error
indication from the device -- but goodness knows if it actually carries
out the command.

Alan Stern

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