Changing SAN Fabric from Dynamic to Static and vice versa

[chuckk281]

Markus had a SAN question from a customer:

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Does anybody have any experiences in changing the login distribution for SAN Fabrics?

Will there be a re-login after this change or will the new setting be effective for all following

Logins? Customer wants to change this but is scared to loose connectivity for the running hosts.

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Olivier and Alex responded:

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Olivier: 

I have already successfully modified it on customer site, (dynamic to static then to dynamic to redistribute the login).

The operation must be done on the first fabric/module, and then all servers must be checked to ensure that all multipathing/paths are in a good state.

Only if all paths are operational could you operate to the second fabric/module.

Markus asked: 

So you had a re-login of the ports? Meaning that they lost the path for some seconds after you changed the setting?

Alex replied: 

This really depends on the type of the VC-FC module and original configuration, i.e. how many uplinks were in the Fabric definition.

When Static mapping is utilized, as you know, each server is mapped to a specific uplink, in a one-to-one relationship. Once you change to Dynamic, each of the servers would have to be re-mapped to a group of uplinks in a SAN Fabric definition. Then VC-FC module will decide which uplink to use for which server depending on the number of servers that are logged-in at that time. As a result, not only your server would have to log back in, i.e. short outage due to server logging out and logging back in, but it also may login via different uplink port.

As Olivier suggested, make sure you have both paths present before attempting this change on the live servers and ensure that one paths comes back online before making changes in the second path.

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Have you done this before? What did you do and how did it work?