Re: READ CAPACITY 16

James Bottomley
2008-12-17T19:36:48Z

On Wed, 2008-12-17 at 12:32 -0700, Matthew Wilcox wrote:
> On Wed, Dec 17, 2008 at 02:14:09PM -0500, James Bottomley wrote:
> > On Wed, 2008-12-17 at 12:11 -0700, Matthew Wilcox wrote:
> > > On Wed, Dec 17, 2008 at 02:04:52PM -0500, James Bottomley wrote:
> > > > Actually, we can't afford to send READ CAPACITY(16) to failing devices;
> > > > some of them never come back.
> > >
> > > When you say 'never come back', do you mean:
> > >
> > > a) The drive discards the command silently
> > > b) The drive hangs until a reset is issued
> > > c) The drive hangs until it's power-cycled
> > > d) The drive turns into a paperweight
> >
> > All of the above ... this is USB ... well, I don't *know* of a D
> > case ... but I wouldn't bet one doesn't exist.
>
> The unfortunate thing is that we don't have a collection of INQUIRY
> results from these devices, so we can't say whether checking for SCSI_2
> would eliminate those in categories C and D.
>
> Are you willing to take a patch that sends RC16 for devices claiming
> SCSI_2, and falls back to RC10 if that doesn't work? Or shall I try to
> implement algorithm D and talk to T10?

Not really ... SCSI_2 is where the problems are. SCSI 3 would be much
more acceptable. Then you can add an inquiry passthrough to USB
mangling for devices you need to work.

James