Subject: iSCSI: Representing iSCSI devices on FC fabrics

From: Robert Grant <[email-masked]>
Date: Thu, 15 Nov 2001 13:40:40 -0700

Hello all,

			I have a question on the representation of iSCSI
devices into Fibre Channel fabrics for an iSCSI-to-FC "gateway" device and
would like to solicit people's thoughts on how best to do this. A gateway
device will allow iSCSI devices and FCP devices to access each other, but in
order to do this a consistent representation of the devices is needed. I
haven't been able to reconcile the iSCSI and FCP standards using what's
currently in the iSCSI standard, and wanted to see if there was any support
to expanding the iSCSI standard to address this (a standard solution is, of
course, much more preferred to every gateway vendor doing it in their own
proprietary way). In particular, how would an iSCSI device map onto Fibre
Channel's World Wide Name (WWN)? Would every device have its own WWN, or
could many iSCSI devices use a single WWN? There have been some discussions
(for example, there was even discussion of including a WWN field in the
iSCSI Login for a Gateway to proxy with in
http://www.pdl.cmu.edu/mailinglists/ips/mail/msg01616.html), but what is the
current view?

			A first approach might be that many iSCSI devices
could use a single WWN. This can work well for FC-AL devices "directly
attached " to the IP network or for small FC fabrics - and where the
predominant interconnect and management of that interconnect is the IP
network. 

			This approach views the FC fabric as flat (or at
least perhaps that FC zoning is "turned off"). As the FC fabric gets bigger,
though, this first approach can create two layers of management - one must
first configure the FC network and then configure the IP network (since the
individual iSCSI devices sharing a single WWN can only be zoned as a group).
The two layers are first "this group of iSCSI devices can access this zone"
on the FC side and then "this iSCSI device can access this FC device in this
zone" on the iSCSI side. If there was a clean integration with FC zoning
(and associated management of the FC zoning), this may be avoided. 

			A further complication is that, as the FC fabric
gets even bigger, a single iSCSI device could end up with multiple entry
points (i.e. paths through multiple gateways) into a single FC fabric. Is
there any common way to represent iSCSI devices (for instance, with respect
to WWNs) that allows the unique identification of that iSCSI device - even
though there are multiple entrypoints onto the FC fabric? The case of
multiple gateways (possibly from different vendors) is the clearest example
of the need for a standard.

			Thank you for your time and I look forward to all
comments/suggestions.

Regards,
Rob
 
Rob Grant
McDATA Corporation

---

From: Thanu Skariah <[email-masked]>
Date: Fri, 16 Nov 2001 12:41:49 +0530

Robert,

    iSCSI allows different naming formats, of which one format is the EUI
format  (See the example
in sec 2.2 .7 and the naming draft -
http://www.ietf.org/internet-drafts/draft-ietf-ips-iscsi-name-disc-02.txt )

    The EUI representation  is of the form eui . <WWN>.  Each FC device's
WWName
can be used to form the corresponding iSCSI name for the device.  This is what
we are
doing on a linux based software FCP/iSCSI gateway that we are implementing, and
this
is why :

(From the naming and discovery draft ):

BeginQuote "

Type "eui." (IEEE EUI format)

   The IEEE iSCSI name might be used when a manufacturer is already
   basing unique identifiers on World-Wide Names as defined in the SCSI
   SPC-2 specification.

   It may also be used by a gateway representing a Fibre Channel or
   SCSI device that is already adequately identified using a world-wide
   name.

" End Quote

Thanks,
Thanu