Re: RES: RES: AS2105-based enclosure size issues with >2TB HDDs

Alan Stern
2014-08-27T14:45:53Z

On Wed, 27 Aug 2014, Oliver Neukum wrote:

> > I don't think we want to add another SCSI flag to say that READ
> > CAPACITY(10) is unreliable.
>
> Why not? It would only be friendly to tell the upper layer
> of a malfunction if we know about it.

To what end? What will the upper layer do with this information?

> > Given the difficulty of determining the true capacity, I see two
> > alternatives. We could set the capacity to a ridiculously large value
> > (like 1 billion TB), or we could leave the capacity set to the low
> > value and disable the "block within bounds" checks. Neither of these
> > is attractive and they both have issues of their own -- although the
> > second is close to what Windows does.
>
> That seems to be the most attractive solution to me.

I'm skeptical that you can convince the SCSI and block-layer developers
about this. Maybe they'll accept it if it is applied only to USB
transports...

> > (For example, udev often tries to read the last sectors of a new drive,
> > looking for a GPT or RAID signature. That won't work if the capacity
> > is set to some random value.)
>
> Yes, but clipping has its own dangers. Suppose you use the medium
> without a partition table.

What would Windows do? In the absence of a partition table, it would
believe the value from READ CAPACITY, right? Isn't that the same as
clipping?

Alan Stern