SCSI-2/3 Question -- Format of Target I/D in "Read Element Status"

[Charles Monia 237-6757]

* From the SCSI Reflector, posted by:
* Charles Monia 237-6757 <monia at AM.SHRMSG.SHR.mts.dec.com>
*
Hi:


In working with SCSI Medium changers, we have noticed two =09
interpretations for the SCSI bus address field in the Read Element Status
data for tape drives. As shown in table 339 of SCSI-2, draft revision 10k=
,
this field indicates the drive's SCSI target ID when it is on the
same bus as the medium changer. The description of the field in
the draft standard is:

        "The SCSI bus address field, if valid, provides the SCSI address
        (binary representation) of the primary device served by the
        medium changer at this element address"

The question of interpretation is over "binary representation".

Most robots that We've seen put the binary *value* of the
address in the field.  One, has elected to treat the field as a       =20
bit mask, with the appropriate bit set for the address.  For example
given a drive at SCSI I/D 3 most will use:

        |  7  |  6  |  5  |  4  |  3  |  2  |  1  |  0  |
        +-----+-----+-----+-----+-----+-----+-----+-----+
        |  0  |  0  |  0  |  0  |  0  |  0  |  1  |  1  |
        +-----+-----+-----+-----+-----+-----+-----+-----+

But the drive in question uses:

        |  7  |  6  |  5  |  4  |  3  |  2  |  1  |  0  |
        +-----+-----+-----+-----+-----+-----+-----+-----+
        |  0  |  0  |  0  |  0  |  1  |  0  |  0  |  0  |
        +-----+-----+-----+-----+-----+-----+-----+-----+

Which of the above is correct?

In researching this question, I discovered that the SCSI-3 SMC draft stan=
dard
(rev 5, subclause 6.5.6, pp46) defines this field and the logical unit fi=
eld as
follows:

"The SCSI bus address field, if valid, provides the SCSI address (binary
representation) of the primary device served by the medium changer at thi=
s
element address.

The logical unit number field, if valid, provides the logical unit number
within the SCSI bus device of the primary device served by the medium cha=
nger
at this element address.
....
Editors note =97 The SCSI bus address and logical unit number fields are =
too
small for SCSI-3."

Has there been a proposal to address the issues pointed out by the editor=
's
note?

Thanks,
Charles


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* Charles Monia Storage Architecture Group                         *
* Digital Equipment, Shrewsbury MA   Internet: monia at shr.dec.com   *
* Tel: (508) 841-6757    X400: c=3DUS; a=3DMCI; o=3DDigital; ou=3DSHR    =
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* Fax: (508) 841-6100                                              *
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