Re: Large disk drives

[Alan Stern <stern@rowland.harvard.edu>]

On Thu, 6 Nov 2014, Boaz Harrosh wrote:

> On 11/06/2014 05:54 PM, James Bottomley wrote:
> > 
> > We don't have a failure.  This is the problem.  Determining that a
> > problem exists 
> > 
> 
> OK Sorry. I assumed the bridge is smart enough to do nothing,
> 
> ie READ_CAPACITY_10 is passed as is via sata to the device that
> actually supports READ_CAPACITY_16, as I understand then the 
> actual good drive is not suppose to send size-modulue-2G in
> response to READ_CAPACITY_10. Should it ?

The bridge does not send SCSI commands to the drive; it sends ATA 
commands.

When the bridge receives a READ CAPACITY(10) command from the host 
computer, if the drive's actual capacity is >= 2^32 blocks then the 
bridge is supposed to send back a result buffer containing 0xffffffff.  
Not the actual capacity modulo 2^32.

> Then the bridge just sends that back to me, now if I send
> READ_CAPACITY_16 the bridge will return NOT-SUPPORTED because
> it is unexpected.

Yes.

> But what are you saying that the bridge was smart enough to
> do READ_CAPACITY_16 get a 64bit value from the drive and then
> return the lower 32bit to me ? Really ? I would not imagine
> in the life of me someone so dumb. And surly it is against
> any spec.

The bridge does not send READ CAPACITY(16) to the drive.  It sends an 
ATA command -- and it probably sends the same command for READ 
CAPACITY(10).

> Are you sure ? I think you are wrong I think the guy reported
> that he can only see 2T out of his 3T drive which means the
> bridge returned 0xffffffff, exactly 2T

We are sure.  Dale reported that the size he got was less than 2 TB, 
and it was equal to the actual capacity modulo 2^32.  You can check for 
yourself; here's the original email:

	http://marc.info/?l=linux-scsi&m=140908235510961&w=2

Alan Stern