Aliases - FC, Device, Global...?

Unanswered Question
Mar 9th, 2007

Does anybody know the difference between FC aliases, Device Aliases and Global Aliases?


The FC (aka zone?) aliases are held in the running config on the switch and also seem to be specific to a VSAN.


Global Aliases seem to be a Fabric Manager thing - does the Fabric Manager server hold a database of aliases so that they are still recognised if you plug the device into a seperate physical SAN managed by the same FM server? Presumably if you connect via a different FM server to the same switch you would get different global aliases because you are connecting to a different database?


Device aliases seem to be an extension of fc aliases (in that they are stored in the running config) that are not VSAN specific and are not restricted to being used for zoning only.


Is that about right? Which of the above are people using and how do you find it? I'm still using fcaliases, purely because I haven't tried the others, although Device Aliases looks like an interesting option...


Thanks,


Allan.

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colin.mcnamara Fri, 03/09/2007 - 08:42

A fcalias can summarize multiple devices in a zone.

http://www.cisco.com/en/US/products/ps5989/products_command_reference_chapter09186a00801470a8.html#wp1242422


A device alias is pretty much the same, but is used in the higher level application functions of the mds.

A great example is that there is a CFS application for distributing device aliases, where I don't think i have seen one for distributing fcaliases. It is also used to reference items in the storage services module.


You are right, global device aliases are a function of fabric manager, but can be used as a tool to migrate from fcaliases to device aliases.


If this was helpful please score this post.

--Colin

a-watkins Fri, 03/09/2007 - 09:04

So is it true that there is no advantage to choosing to use fcaliases if device aliases are available (presumably restricted by SAN-0S version, Dev aliases being introduced later..?)? And fcaliases are only there for backward compatibility now?


Allan.

colin.mcnamara Fri, 03/09/2007 - 10:39

The place I would use fcaliases would be the CCIE lab ;)


There might be a specific gotcha with something like ficon (I don't really deal with it, and cannot say). But other then that, device aliases are very nice. Especially the CFS integration.

setmason Tue, 03/20/2007 - 07:10

You can find a pretty good description and usage in the MDS Cookbook http://www.cisco.com/application/pdf/en/us/guest/products/ps6039/c1067/ccmigration_09186a008054084e.pdf.


Device aliases and FMS Global Device Aliases are the same thing (FMS just added the word Global).


The problem with fcaliases (that device aliases solves) is that with fcaliases I could have the same alias defined in two different vsans with a different pwwn in each pwwn. Secondly, fcaliases are only restricted to zoning. Not IVR, not QOS, not CLI output (like with 'show fcns' or 'show flogi'..)


In SANOS 3.1(2), you can make a zone member of type enhanced device alias. This means that now if you swap out the hba you only have to change the device alias database, and not modify the zones. Think of it like updating the dns server with a new IP address, you don't have to tell everyone that your new hostname is www.xyz.com b/c www.abc.com failed.



a-watkins Tue, 03/20/2007 - 08:09

So in fact device aliases are global aliases? The device aliases are held in a database that each switch has a copy of?

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