Re: Problem with USB-to-SATA adapters (was: AS2105-based enclosure size issues with >2TB HDDs)

Alan Stern
2014-08-31T14:13:44Z

On Sat, 30 Aug 2014, Douglas Gilbert wrote:

> On 14-08-30 05:15 PM, Alan Stern wrote:
> > On Fri, 29 Aug 2014, Matthew Dharm wrote:
> >
> >> Is there an 'easy' way to override the detected size of a storage
> >> device from userspace? If we had that, someone could write a helper
> >> application which looked for this particular fubar and try to Do The
> >> Right Thing(tm), or at least offer the user some options.
> >
> > You mean, force a Media Change event and override the capacity reported
> > by the hardware? I'm not aware of any API for doing that, although it
> > probably wouldn't be too hard to add one.
> >
> > How would the user know what value to put in for the capacity? Unless
> > the drive had been hooked up to a different computer and the user
> > manually noted the correct capacity and typed it in, it would have to
> > be guesswork.
>
> Might another possibility be using the SAT layer to issue
> the appropriate ATA command via the SCSI ATA PASS-THROUGH
> (12 or 16) command to find out the disk's size.

That might work. Not all USB mass-storage devices support ATA
pass-through but some of them do.

> This might
> be a possible strategy if READ CAPACITY(10) yields 0xffffffff
> for the last sector's LBA and the follow-up READ CAPACITY(16)
> fails or yields a truncated value.

Yes. The problem in this case is that READ CAPACITY(10) yields a
reasonable value (not 0xffffffff), so READ CAPACITY(16) never gets
sent. And if it was sent, the device wouldn't handle it anyway.

> BTW Been looking at a USB-to-SATA adapter that uses the
> UAS(P) transport. I thought nothing could have worse
> SCSI compliance than USB mass storage devices. I was
> wrong ...

Well, a USB-to-SATA adapter _is_ a USB mass-storage device. What
vendor and product?

Alan Stern

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