System Probing with SCC lun devices

[Larry Chen]

* From the SCSI Reflector (scsi at symbios.com), posted by:
* Larry Chen <larryc at maxstrat.com>
*
Hi James,

Thanks for your reply. I have added additional comments
below.

On Fri, 3 Jan 1997 16:21:38 -0500  James Smart USG wrote:
>
>Hi Larry,
>
>You don't have to be a SCC peripheral driver to send
>a Report Luns command.

Reality check. The Report Luns command is mandatory
only for the SCC device type. I don't think it is common
practice to issue unsupported SCSI commands during 
System probing. The Lowest Common Denominator (lcd) approach 
is "commonly" followed (in order to support all the
various peripheral device types and all SCSI I, II, and III levels).

The safest (i.e. lcd) approach would be something like the
following:

After a first stage probe (i.e., say 0-63 luns), the second 
stage probe could send the Report Luns command to only the 
SCC luns in order to finish populating the CAM edt. That
why I originally stated the SCC driver had to be part
of the configuration driver - because the second stage probe
is SCC aware.

Bye for now.
Larry

>In most cases, the probing element is
>independent from the peripheral drivers (so that the appropriate
>drives can thereafter attach to the appropriate device that's
>known to be in existence) or each peripheral driver is told to
>look at the device and see if it recognizes the device. 
>As such, the probing element can pick and choose the commands
>used to complete the probe.
>
>So, using Report Luns seems reasonable to me. I do wonder if there's
>a better way than trial and error to determine when it's best to
>use Report Luns. The basic assumption being that Report Luns is only
>present on a SCSI-3 device. If Lun 0 returns a type indicating SCSI-2
>(which also means it may not indicate an SCC device type) what's the
>best method to continue probing with ?
>
>-- James
>
>
>------- Begin Forwarded Message
>
>Date: Fri,  3 Jan 97 12:19:09 PST
>From: Larry Chen <larryc at maxstrat.com>
>Subject: System Probing with SCC lun devices
>To: scsi at symbios.com, serial_solutions at zk3.dec.com
>Sender: owner-serial_solutions
>
>*
>* From the serial_solutions Reflector, posted by:
>* Larry Chen <larryc at maxstrat.com>
>*
>* To post to this Reflector, send email addressed to serial_solutions at zk3.dec.com
>*
>
>In a typical System probing methodology, the
>configuration driver must probe for luns and populate
>the equipment device table (edt in CAM terminology)
>before any of the other peripheral device drivers are 
>initialized.
>
>It has been suggested that the Report Luns command
>can be issued to SCC lun to determine the
>the other non-SSC lun(s) that are behind the array
>controller device.
>
>If this is the case, the SCC host driver must now be
>part of the configuration driver. The SCC host driver
>must issue a Report Luns command and populate the
>equipment device table (edt in Cam terminology) before
>any of the Non-SCC drivers are initialized (and claim
>their luns).
>
>Is this an acceptable System probing methodology for
>the System folks?
>
>Regards,
>Larry
>----------------------------------------------------
>Larry Chen                 Tel: 408.383.1600 (x116)
>Maximum Strategy, Inc.     Fax: 408.383.1616
>801 Buckeye Court       E-mail: larryc at maxstrat.com
>Milpitas, CA 95035
>----------------------------------------------------
>
>------- End Forwarded Message
>
>
>James Smart                                            email: smart at zk3.dec.com
>Alpha UNIX Systems - Digital Equipment Corp.           Phone: 603-881-2472
>110 Spit Brook Road,    Nashua, NH  03060              Fax  : 603-881-2257
>Disclaimer: My statements and opinions reflect my own thinking and are not
>   necessarily reflective of any employer or association.
>



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