RE: iSCSI: DLB's Comment on SCSI Port Names

["Julian Satran" <Julian_Satran@il.ibm.com>]

Marjorie,

Thanks for your complete and timely answer.

Regards,
Julo

"KRUEGER,MARJORIE (HP-Roseville,ex1)" <marjorie_krueger@hp.com> 07/11/2002 05:15 AM Please respond to "KRUEGER,MARJORIE (HP-Roseville,ex1)"

To:        Julian Satran/Haifa/IBM@IBMIL         cc:        ips <ips@ece.cmu.edu>         Subject:        RE: iSCSI: DLB's Comment on SCSI Port Names

Julo,
I'm a bit confused as the issues list on your website does not have this as issue 37, and all I see is issue 9 (where your comment appears to imply "no change"?)
 
In any case, here's what I recommend:
 
In sec 1.1 Definitions change the following definitions to:
 
I_T Nexus:  the last sentence should be
 
The I_T nexus can be identified by the conjunction of the SCSI port names; that is, the I_T nexus identifier is the tuple (iSCSI Initiator Name + ',i,'+ ISID, iSCSI Target Name + ',t,'+ Portal Group Tag).
 
SCSI Port Name: definition should be
 
A name made up as UTF-8 characters and includes the  iSCSI Name + ',i,' or ',t,' + ISID or Portal Group Tag
 
In sec 2.2.7, 1st paragraph, delete the comment in parenthesis starting with "(for iSCSI,.." (or change it to point it to section 2.4.2, your choice).
 
In sec 2.4.2, change the text to:
 
  When used in SCSI parameter data, the SCSI port name MUST be encoded as:
      - The iSCSI Name in UTF-8 format, followed by
      - a comma separator (1 byte), followed by
      - the ASCII character 'i' (for SCSI Initiator Port) or the 
       ASCII character 't' (for SCSI Target Port), followed by 
      - a comma separator (1 byte), followed by
      - A string representation (<numerical-value>, see section 4.1 Text Format)
       of the ISID (for SCSI initiator port) or the portal group tag (for SCSI target port).
       SCSI port names have a maximum length of 255 bytes.
       The ASCII character 'i' or 't' is the label that identifies this port 
       as either a SCSI Initiator Port or a SCSI Target Port.
The 255 max port name makes for a 237 max iSCSI node name (check my math Jim :-) as the max character representation of an ISID is 15 characters for the largest decimal representation (14 char for the largest hex), + 3 char (",i,") + 237 = 255
 
The change in max node name causes changes to:
 
sec 2.2.6.1, paragraph 2, 
sec 2.2.6.2, 2nd p, 3rd bullet
 
I will see that a change is proposed to Annex A in whatever SAM doc is currently under revision.
 
Thanks,
Marjorie Krueger
Networked Storage Architecture
Networked Storage Solutions Org.
Hewlett-Packard
-----Original Message-----
From: Julian Satran (Actcom) [mailto:Julian_Satran@actcom.net.il]
Sent: Tuesday, July 09, 2002 6:44 AM
To: KRUEGER,MARJORIE (HP-Roseville,ex1); 'Jim Hafner'; Black_David@emc.com
Cc: ips
Subject: Re: iSCSI: DLB's Comment on SCSI Port Names

Marjorie,
 
I'll list this as issue 37 and I think we can settle on 249 :-)
I would appreciate if you let me know what constants change (in 2.4.2?)
 
Julo
----- Original Message ----- 
From: KRUEGER,MARJORIE (HP-Roseville,ex1) 
To: 'Jim Hafner' ; Black_David@emc.com 
Cc: ips@ece.cmu.edu 
Sent: Tuesday, July 09, 2002 4:04 AM
Subject: RE: iSCSI: DLB's Comment on SCSI Port Names

I've just encountered this issue with regards to iSCSI port name encoding in the SCSI MIB, and the currently specified port name encoding causes inconvenience (at best).  IMO, it makes sense to be able to treat an iSCSI name field, be it device name or port name, the same - as a string of display characters, portions of which may contain ASCII-encoded numeric values.
 
I don't really see that it makes a difference whether one views ISID and TPGT as numeric strings or values, since as Jim says, there are no calculations performed using these things, and they are basicly just "tags".  The issue for me is that the rest of the "SCSI port name" is a string and I see no value in "encoding" the ISID or TPGT as a value for SCSI purposes, as SCSI should have no need to use the ISID or TPGT values separately from the entire port name.  And even if SCSI had such a need, it's a simple matter to convert a numeric string representation to a value.
 
The downside of a string-encoding is the increased maximum size of the SCSI port name.
 
If strings over 256 characters are a problem for some platforms, I'd be in favor of reducing the max iSCSI node name to 249 characters so the maximum SCSI port name would be 255 characters total (249 char name + ",i," + "0x0000")
 
Marjorie Krueger
Networked Storage Architecture
Networked Storage Solutions Org.
Hewlett-Packard
-----Original Message-----
From: Jim Hafner [mailto:hafner@almaden.ibm.com]
Sent: Monday, July 08, 2002 9:08 AM
To: Black_David@emc.com
Cc: ips@ece.cmu.edu
Subject: RE: iSCSI: DLB's Comment on SCSI Port Names


David, 

I believe it will (may?) be used, so I agree we're in the second case.  However, this format is the intended use in SCSI protocol stuff.  Two places where SCSI ports names are used now is in ALIAS, Access Controls and in third party reservations -- see caveat below, however) 

I don't see a need in this context to define these as strings (that's not a SCSI way of thinking...).   

However, I think the issue comes down to a simple question:  are the ISID and TPGT values or numerical strings (Julian is calling them numerical strings, but I've always thought of them as values, in spite of the fact that there is no arithmetic done on them - there is precedent in SCSI for such thinking, so I'm not completely out in the woods here). 

If they are values, then I'd like to see them formatted for SCSI in "value form";  if they are strings, then any representation should be OK. 

Does that at least get to the core of the issue?

Jim Hafner

CAVEAT: I don't think we'd use the iSCSI constructed port names in those contexts as device names are better suited for those purposes, but these are examples where specification of SCSI port name format is required.

To:        Jim Hafner/Almaden/IBM@IBMUS
cc:        ips@ece.cmu.edu
Subject:        RE: iSCSI: DLB's Comment on SCSI Port Names



Jim,

My view of this is that either:
- The SCSI Port Name is never going to be used, in which case
it shouldn't be designed to this level of detail. OR
- It's going to be used, and hence is worth designing in a fashion
that is reasonable to use.
I think we're in the second category, and turning the ISID into
hex ASCII (well, UTF-8) so the SCSI port name is a string is
worth doing now to avoid problems when people actually try
to use it.  I would have no problems if someone wanted to
pad the string, but I'd make specifying the padding the
responsibility of the protocol/API/situation in which it
was used rather than incorporating the padding into the name.

Thanks,
--David

-----Original Message-----
From: Jim Hafner [mailto:hafner@almaden.ibm.com]
Sent: Monday, July 08, 2002 11:42 AM
To: Black_David@emc.com
Cc: ips@ece.cmu.edu
Subject: Re: iSCSI: DLB's Comment on SCSI Port Names



David,

You wrote:

>[T.9] 2.4.2  SCSI Architecture Model
>
>  The SCSI Port Name is mandatory in iSCSI. When used in SCSI
>  parameter data, the SCSI port name MUST be encoded as:
>  - The iSCSI Name in UTF-8 format, followed by
>  - a comma separator (1 byte), followed by
>  - the ASCII character 'i' (for SCSI Initiator Port) or the
>    ASCII character 't' (for SCSI Target Port), followed by
>  - a comma separator (1 byte), followed by
>  - zero to 3 null pad bytes so that the complete format is a
>    multiple of four bytes long, followed by
>  - the 6byte value of the ISID (for SCSI initiator port) or the
>    2byte value of the portal group tag (for SCSI target port) in
>    network byte order (BigEndian).

> That's a peculiar format with padding nulls in the middle and
> a number concatenated after the padding - for example, it can't
> be passed in iSCSI login without format conversion.  How about
> converting the number to 4 or 12 bytes of hex (ASCII characters)
> and moving the padding to the end so the result is actually a
> string, and excluding the padding from the definition of the name?
> This will increase the maximum length of port names, but produce
> names that are easier to deal with.

Admittedly that's an odd format, however here was the reason for this
layout.
1) it's not used directly in iSCSI "Text" strings; it's intended to be a
description of how this information is packed into a byte array for
representation in "SCSI parameter data" (as it says!) -- that is, it's NEVER
"passed in iSCSI login" (in this form).
2) the padding after the string was to force the binary values of the ISID
or PGT to be better word aligned and can be more easily extracted as a value
direct from the byte array without conversion.

What do you think?

Jim Hafner