97-234r0 -- LUN_Z Capabilities Bit in SPC-2

ROWEBER at acm.org ROWEBER at acm.org
Fri Aug 29 07:40:45 PDT 1997


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* ROWEBER at acm.org
*
                                                              T10/97-234r0
 
    Date:	21 August, 1997
    To:		T10 Membership
    From:	Ralph Weber, X3T10 Alternate member from Symbios Logic
    Subject:	LUN_Z Capabilities Bit in SPC-2


Problem Statement

SCC and SCC-2 require the logical unit at LUN=0 to have a device type of
'storage Array controller device' (0Ch). However, many operating systems
require the LUN=0 unit to have a device type of 'direct access' (00h) or
'sequent- ial access' (01h) for the purposes of their configuration
scanning code.  Also, there is no reason why a RAID device cannot have a
virtual unit at LUN=0.

I have submitted a letter ballot comment, which if accepted will change
this.  Yet, additional changes are needed in SPC-2 to support the proposed
letter ballot change in SCC-2.

Proposed Changes

A bit must be defined in the Standard Inquiry Data that, when set,
indicates that the logical unit supports the SCC command set in addition to
the command set identified by the device type.  It is recommended that this
bit be called LUN_Z and that it be bit 0 in byte 5.

In Table B.2 (the operation code numerical list), O (for optional) must be
added in the D (disk), T (tape), W (write-once), O (optical), M (medium
changer), and E (enclosure) columns for the following commands:

	A3h	MAINTENANCE (IN)
	A4h	MAINTENANCE (OUT)
	BAh	REDUNDANCY GROUP (IN)
	BBh	REDUNDANCY GROUP (OUT)
	BCh	SPARE (IN)
	BDh	SPARE (OUT)
	BEh	VOLUME SET (IN)
	BFh	VOLUME SET (OUT)

Note: It would be nice to be able to include the R (CD-ROM) column in the
list above.  But, this is not possible because CD-ROM defines several of
these operation codes for other uses.  Perhaps this can be resolved as part
of the DVD work.  Otherwise, it will not be possible to have LUN=0 be both
a CD-ROM device and a RAID controller device.  If no resolution can be
reached, perhaps giving software developers sufficient notice of this
restriction will allow them to design system configuration scanning code
that deals with it.
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