Serial support of RESERVE(6)/RELEASE(6)

scheible at scheible at
Mon Jun 17 11:04:25 PDT 1996

* From the SCSI Reflector, posted by:
* scheible at VNET.IBM.COM
I have placed this note on the SCSI and SSA reflectors.  Sorry for any

   How can serial interfaces support 3 bit addresses?

   Currently SPC and SBC state that RESERVE(6) and RELEASE(6) are
mandatory (for block devices).  However, these commands only have a
3 bit address.  This means that S3P(SSA), FCP (FC), SBP (1394) and
even 16 bit SCSI cannot address all possible devices (only 8).
Fortunately, RESERVE(10) and RELEASE(10) fix this problem by using
a 64 bit address.

   SSA uses an 8 byte Unique ID (IEEE address) as the device ID for
SAM.  FCP maps a port address into the 8 byte field.  I did a quick
scan of FCP and SBP and could not find any mention on how to address
devices in these commands.  Can anyone help on this issue?

   I can see several solutions:

1) Make the command support transport layer specific, then the serial
   interfaces can support RESERVE(10)/RELEASE(10) and not support the
   6 byte versions.  This requires X3T10 support.

2) Take a literal translation (like 16 bit SCSI) and only support
   devices 0000000000000000h thru 0000000000000007h.  In SSA, since
   the high bits are a company ID, this would not allow most (all?)
   companies from use this command.  In 16 bit SCSI, you can only
   Reserve/Release the low 8 devices.

   Anyone have any input?

John Scheible
scheible at

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