Fabric Migrations – Thoughts & Considerations


As time passes hardware life cycles come to an end.  With the purchase of new equipment customers, contractors, and the companies supplying replacement hardware are faced with the task of making physical changes to production environments. Physical changes made are in the form of replacement of storage arrays, fabric switches, and in some situations a parallel server consolidation effort.  This post will discuss the planning considerations for making a physical cut over from an old SAN fabric to a new fabric.

Premise: New director switches have been purchased and all production servers need to migrated from the old to the new fabric.
Assumption: A storage migration plan has been established and has been kicked off.

Note: depending on the storage vendor and tools available cut over to the new fabric may occur before, during, or after the storage migration.

Before: New storage arrays are added in line on new fabric and data migration is performed array to array.
During: Hosts are migrated to new fabric once a back end data migration has been completed (array to array).
After: Data migration completed prior to cutting over hosts to new fabric.

Key questions need to be addressed and documented before approaching a fabric migration

– What OS’s are present within the SAN environment?

– Do all hosts have redundant paths to disk?

– Are all clusters identified and accounted for?

– Are any hosts using disk from multiple storage arrays?

– Have all host connections been audited/confirmed in terms of alias to host HBA WWN association?

– Determine physical location of ALL hosts which will need to be migrated.

– Are all host os versions and patch levels supported by the new hardware (hba, server os, etc.)

– Audit zone sets, confirm all host alias values, delete all bad/old zone sets.

Special attention should be paid to HP-UX hosts.  If HP-UX hosts do exist the new and old SAN fabric will need to have identical switch domain ID’s. This is due to the fact that HP-UX hosts include the connected switches domain ID in the recognized path to disk.  Bottom line, if you have HP-UX hosts identify which switches they are on and ensure that you have identical domain ID’s on switches the hosts will be migrated to/from.  This will remove a lot of headaches when performing the fabric migration for HP-UX hosts.

Fabric Merge (migrate Zones & aliases)

Zoning Impact:  Hard Zoning Vs. Soft Zoning

With Hard Zoning all zones will need to be recreated based on the new ports which will be used by hosts.

With Soft Zones the prospect of merging a fabric and simply moving the hosts drop becomes and option.  Provided  zone sets and host aliases migrate successfully.

“Cold” cutover: shut down everything and migrate fabric drops

“Hot” cutover: Merge fabrics by connecting new and old fabric switches via ISL (Not compatible in installations where HP-UX is in use).  Switches new and old must be compatible.

Brain dump in progress…

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