RE: iSCSI Naming: WWUIs, URNs, and namespaces

[Black_David@emc.com]

> So from what I see from your example is iSCSI.Example.Com returns the WWUI
> via SCSI that is then inserted into the domain to obtain the desired IP.

No for a couple of reasons:
- The WWUI is not inserted into the domain.  The WWUI is an identifier,
	not an address, and extracting its DNS portion and contacting that
	host will not generally result in anything useful happening.
- The IP is the *same* as iscsi.example.com, because the Send Targets
	command instructs whatever machine has been contacted to send	
	a list of targets that are exported from that machine.
Note that the machine contacted could be foo.example.com (it doesn't
have to be iscsi.example.com) as  the "iscsi" is the iSCSI target name
sent in the iSCSI login command - it's not part of the DNS hostname.

> As example [WWUI].example.com which is not World Wide Unique
Identification but
> at least unique to example.com.  Why are you describing this process as
> reverse DNS?  If this is the process then I find the term reverse DNS
> confusing. 

Because the actual name returned would be something like
com.example.example7 - since the DNS components are reversed, the
naming authority is referred to as "reverse DNS".  Note that the name need
not contain the name of the machine returning them - com.example.example7
could be returned from iscsi.example.com, foo.example.com, or
bar.example.com, BUT if more than one of them returns it, it MUST be the
same target every time.  So, one could connect to foo.example.com, do
an iSCSI login to the "iscsi" target at foo.example.com, send it the
"Send Targets" command, and get back com.example.example1,
com.example.example2, etc.  All of these are separate targets
behind the same communication endpoint at foo.example.com.

> You are referring to a conventional alias.

No, it's not alias.  "iscsi" is a canonical target used by iSCSI -
none of the aliases listed in your message could be used in its place
with the expectation that something useful would happen (e.g.,
logging into the "archie" iSCSI target will not yield access
to the Archie service - why on earth would one want to tunnel
Archie over iSCSI?). It's a unique name for one of the targets behind
this  communication endpoint.  

> As this one machine
> may not be able to carry the load for all clients or connect to all
targets,
> would you then break connection to the iSCSI machine and then make direct
> connections to the LUNs?

Break the connection -Yes.  For communication load reasons -
not necessarily, as the connection can only be used to retrieve
target identifiers and can't access LUs.  To connect to a LUN - No,
the names returned name iSCSI targets, all of which share this
communication endpoint.   The session over which "Send Targets"
was sent is only useful for "Send Targets" because it's logged into
the canonical iSCSI target, which is only good for that purpose.
To access the actual targets, a new connection to foo.example.com
and a login to the target (one for each target) would be necessary.

> Would a domain support multiple SCSI portals with
> other names like iscsi1 or iscsi2?  Is that also to be a standard
> convention?

Sure, and I don't see the need to standardize that convention.  If someone
wants
to use blue-suede-shoes.example.com as a storage server that speaks iSCSI,
I don't see any problem.

Hiding behind this is the question of how foo.example.com (or
blue-sued-shoes.
example.com)  was discovered in the first place - the answers to that are to
be
found in the naming and discovery slides Mark used in Minneapolis - static
configuration, SLP, and iSNS can be used for this purpose.

Please read the naming and discovery draft carefully before continuing this
thread.  Much of the above is contained in it.

--David

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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 435-1000 x75140     FAX: +1 (508) 497-8500
black_david@emc.com       Mobile: +1 (978) 394-7754
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