Re: iSCSI Boot: Technical Issues

[Mark Bakke <mbakke@cisco.com>]

Prasenjit-

I like the dashes better.  They would also make it easier to just
specify the part of the LUN structure that is needed. SAM-2 section
4.9 defines three formats for 4-byte LUNs; the first two only use
the first 16 bits, and most implementations only use these.  I still
think that it will be a relatively rare case to use more than the
first four digits.

Can I suggest:

Single-level LUNs (defined in SAM-2 4.9.3) use xxxx; these can
have values up to 0x3fff.

Multiple-level LUNs (defined in 4.9.4) use as many xxxx fields as
they need (e.g. xxxx-xxxx, xxxx-xxxx-xxxx, and xxxx-xxxx-xxxx-xxxx
are all valid; unspecified xxxx are zeroes).  That would fit well
with the way the LUN structuring works in SAM-2; each implementation
uses the number of levels that it needs.

I just noticed that SAM-2 also allows extended single-level LUN
fields up to 8 bytes.  It appears that these are there for single-
level LUN implementations that need to define LUN values greater
than 0x3fff, without using the multi-level LUN structure which was
built mostly for (I think) parallel SCSI gateways.

Anyway, I think that your dash format, allowing for as many sets
of xxxx as needed, would be the ideal LUN format.

--
Mark


> Prasenjit Sarkar wrote:
> 
> 1. Looks like there is no opposition to making this a standard draft.
> 
> 2. After talking to an HCI person in IBM, I have the following proposal:
> 
> We can change the LUN format to be xxxx-xxxx-xxxx-xxxx
> 
> This notation is subtantially better than "xxxxxxxxxxxxxxxx" in terms of HCI errors and is almost
> equivalent to a 16-bit format representation.
> 
> Since most of the numbers are going to be zeros, all we need to do is to edit 1 set of "xxxx".
> 
> I hope concerned parties at both sides are amenable to a resolution, since I have not seen any new
> arguments in the past week,
> 
> Thanks,
> Prasenjit

-- 
Mark A. Bakke
Cisco Systems
mbakke@cisco.com
763.398.1054