Common industry usage? - of op x12 Inq byte 2

Pat LaVarre LAVARRE at iomega.com
Thu Oct 3 12:47:08 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Pat LaVarre" <LAVARRE at iomega.com>
*
> 00h as the SCSI version code
> in response to an Inquiry command.
> Question- How will such a response
> cause comonly available systems to act?
> Will they throw up their hands, ...
> Would it be better to claim compliance, 04h,
> and test ...
 
You might prefer a false claim of 02h over a false claim of 04h or the true claim of 00h.
 
I've been told Windows & Mac don't check byte 2 of op x12 Inquiry data, but that elements of Linux do?
 
When you see Windows/Mac talking SCSI over ATAPI, USB, or FireWire, odds are good that byte is zero there.  Among the slight, pointless, & pernicious binary compatibilities between the SCSI of SFF and the SCSI of ANSI is the SFF requirement to zero that byte.  SFF defined ATAPI before ANSI did, and USB & FireWire storage devices often use more or less transparent bridges to ATAPI.
 
Web trails like the following tell us the standard Linux patch for unintelligible Inquiry data of SCSI over USB substitutes 02h.
 
http://members.aol.com/plscsi/hosts.html
http://lxr.linux.no/source/drivers/usb/storage/
http://lxr.linux.no/source/drivers/usb/storage/unusual_devs.h
http://lxr.linux.no/ident?i=US_FL_FIX_INQUIRY
http://lxr.linux.no/source/drivers/usb/storage/usb.c#L445
 
if ((us->srb->cmnd[0] == INQUIRY) &&
    (us->flags & US_FL_FIX_INQUIRY)) {
        unsigned char data_ptr[36] = {
            0x00, 0x80, 0x02, 0x02,
            0x1F, 0x00, 0x00, 0x00};
 
As you can see, that patch also corrects your byte[4] additional length to say your available length is x24 = 4 + sizeof [4] + x1F, and concludes surely you must want the byte[1] & x80 RemovableMediaBit set.  But I've been told this patch is Not always applied to devices that zero byte 2 of op x12 Inquiry.
 
Fun question, thank you.
 
Pat LaVarre x4402

	-----Original Message----- 
	From: Sullivan, Patrick L [mailto:Patrick.Sullivan at gd-ais.com] 
	Sent: Wed 10/2/2002 4:12 PM 
	To: t10 at t10.org 
	Cc: 
	Subject: Common industry usage?
	
	

	* From the T10 Reflector (t10 at t10.org), posted by:
	* "Sullivan, Patrick L" <Patrick.Sullivan at gd-ais.com>
	*
	        I am working with a group of companies that are developing data
	storage devices used in very closed systems (aircraft with proprietary
	operating systems and interfaces) that will periodically need to be
	connected to standard commercial workstations.  The intent is to use Fibre
	Channel as the connection media and SCSI as the protocol.  Some
	manufacturers will not implement the required complete SCSI command set.
	In these cases, they should report 00h as the SCSI version code in response
	to an Inquiry command.
	
	        Question- How will such a response cause comonly available systems
	to act?  Will they throw up their hands, saying "you're not compliant with
	anything, so I can't talk to you"?  Would it be better to claim compliance,
	04h, and test for any interoperability problems with real systems?
	
	        All systems will support INQUIRY, READ(10), READ CAPACITY, TEST UNIT
	READY commands and will only be used to read data stored via other
	interfaces.
	
	        My company is using a fully compliant interface, so this isn't a
	problem for us directly, however it is a concern for the user community
	interested in these systems.
	
	        Appreciate any thoughts or guidance you might be able to offer.
	
	       
	        Pat Sullivan
	        General Dynamics Advanced Information Systems
	        patrick.sullivan at gd-ais.com
	
	         
	
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