Report LUNs command problem

George Penokie GOP at
Thu Dec 12 13:38:17 PST 1996

* From the SCSI Reflector (scsi at, posted by:
* "George Penokie" <GOP at RCHVMP3.VNET.IBM.COM>
As I was looking at the Report LUNs commands and thinking about the
SCC addressing I realized there is a hole in that command.  The
problem is that an application has no way of knowing the format of the
LUN field if the logical unit is NOT an array controller device.

If the logical unit is an array controller device then the SCC
standard defines the format of the LUN.

This problem occurs because there is more than one format for the LUN
field depending on which physical protocol (SIP, FCP, SBP, SSA) the
reporting device has.

For example: A SIP device would report LUN 1 a value of
01h,00h,00h,00h,00h,00h,00h,00h where a FCP device would report a LUN
1 value of 00h,01h,00h,00h,00h,00h,00h,00h.  This would occur because
FCP devices use a two byte LUN address where SIP only uses a 6 bit LUN

One solution to this problem would be to require all devices that
support the report LUNs command to report LUNs using the SCC
addressing format. With that requirement, in the example above, a LUN
1 would have the value 00h,01h,00h,00h,00h,00h,00h,00h no matter what
protocol was being used by the device.

This is NOT a problem for devices that only have a LUN 0 (98% of the
world). A logical unit with a LUN 0 address always report their LUN
address as 00h,00h,00h,00h,00h,00h,00h,00h.

Any comments?

Bye for now,
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