Re: [storm] iSCSI feature removal: SLP ?

"Mark S. Edwards" <> Mon, 07 June 2010 15:41 UTC

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Date: Mon, 07 Jun 2010 11:59:40 +0100
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From: "Mark S. Edwards" <>
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Subject: Re: [storm] iSCSI feature removal: SLP ?
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Sorry for the delay.

As you say, RFC3721 was more about guidance and was written before 
there was any deployment experience.  At least the text says 'should' 
rather than 'SHOULD'.  It might be nicer to all round if it could 
just be removed and no extended discovery mechanism be mentioned, but 
we have realities to consider such as an iSCSI array won't get 
Microsoft certification unless it supports at least basic iSNS - 
running code and consensus.

The one good thing we have now is that iSNS is indeed now an IETF 
protocol (RFC 4171) and the original argument for SLP was that it was 
an existing RFC.  So the argument for using SLP ahead of iSNS is no 
longer relevant.

So if pushed I'd write something like:

"iSCSI equipment that need discovery functions beyond SendTargets 
should implement iSNS for extended discovery management capabilities 
and maximum interoperability."

Since any unit that implements SLP or even LDAP as a discovery 
mechanism is not going to interoperate with the majority of systems, 
I'd hesitate to even mention them.  However, if anyone feels strongly 
that SLP deserves some mention, then by all means do so, just please 
don't assert it too strongly.

One final point.  Given that iSNS has won the consensus argument, is 
there a case for turning the "should' in the above sentence to "SHOULD" ?


At 23:54 21/05/2010, wrote:
> > Regarding the feature removal discussion, can I add SLP to the list ?
> >
> > The RFC 3721 states
> >
> > "iSCSI equipment that
> >        need discovery functions beyond SendTargets should at least
> >        implement SLP, and then consider iSNS when extended discovery
> >        management capabilities are required such as in larger storage
> >        networks.  It should be noted that since iSNS will support SLP,
> >        iSNS can be used to help manage the discovery information returned
> >        by SLP."
> >
> > The implication is that targets and initiators should expect to find
> > support for SLP before considering iSNS.
> >
> > I remember our first iSCSI appliance and we spent ages trying to get
> > SLP working because it the above wording effectively made it
> > mandatory.  SLP turned out to be a complete bust and was effectively
> > killed off when Microsoft refused to support it in their initiator
> > and in their target logo tests.
> >
> > The result is that today I doubt you could find a target or initiator
> > out there supporting SLP.
> >
> > For anybody that does still implement SLP we could change the wording
> > for SLP a little to remove the implied hierarchy, or just admit that
> > running code has created IETF consensus.
>This is interesting.  RFC 3720 (main iSCSI spec) never mentions 
>SLP.  RFC 3721 is not a Standards Track RFC, but that's not a reason 
>not to update it (if people will excuse the double negative).
>So, Mark, could you send an email to the list with proposed text on 
>SLP that you'd like to see in the new consolidated iSCSI draft (no 
>more than a few sentences, please)?  If that text (as revised) is 
>acceptable to the WG, the result would go into the new consolidated 
>iSCSI draft, and RFC 3721 would be added to the list of RFCs that 
>are being updated by that draft.
>David L. Black, Distinguished Engineer
>EMC Corporation, 176 South St., Hopkinton, MA  01748
>+1 (508) 293-7953             FAX: +1 (508) 293-7786
>        Mobile: +1 (978) 394-7754