Clarification on 8 byte single level LUN format in SPI-4

Kendall, Guy gkendall at
Tue Aug 27 10:08:47 PDT 2002

* From the T10 Reflector (t10 at, posted by:
* "Kendall, Guy" <gkendall at>
The SPI-4 L_Q contains an 8 byte LUN field where the MSB is sent first, and
the LSB sent last. SPI-4 references SAM-2 for the format of the 8 bytes. In
SAM-2 rev. 23, section 4.8, table 1 shows the format of the Single Level LUN
structure. Byte one shall contain the 8-bit LUN, and all other bytes shall
be zero.

I am looking for 100% clarification on which bytes in the SPI-4 table match
up with the SAM-2 table. I thought I understood this, but now it is in
question and I'm looking for clarification.

My question is, in the SPI-4 L_Q, does the MSB correspond to byte zero in
the Single Level LUN format in SAM-2, or to byte 7? Since the actual 8-bit
LUN is in byte one of the single level LUN structure, will this LUN byte be
sent out second or seventh of the 8 bytes?

Guy Kendall

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