Re: iSCSI: Representing iSCSI devices on FC fabrics

[Thanu Skariah <tskariah@npd.hcltech.com>]

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



Robert Grant wrote:

>                         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