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background of D,P (hard) zoning in case FICON

  • 1.  background of D,P (hard) zoning in case FICON

    Posted 11-06-2019 11:02 AM
    Greetings forum members,

    it is an unsaid best practice to use D,P (domain, port) based zoning in case of a FICON environment.

    We have 2499-816 DCX switches with FOS Kernel: 2.6.14.2 , Fabric OS: v8.2.0a, and MainFrame hosts ( linux, z/VM, z/OS ), and currently they're used by domain ID/ port index based zoning.

    We would like to understand the technical background of the best practice recommendation to use D,P (hard) instead of WWPN based (soft) zoning.

    Is there any process within the FOS/SAN operations why the D,P based zoning is a must in case of a FICON environment?

    I appreciate your comments.

    Cheers.

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    Regards, Tamas.
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  • 2.  RE: background of D,P (hard) zoning in case FICON

    Posted 11-07-2019 06:41 AM

    The IODF, built with HCD, effectively does what zoning does. Keep in mind that IBM had to resolve what zoning does with ESCON and the mentality of the mainframe space is that the host controls everything anyway so there was no need to change this. A mainframe knows nothing about WWNs.

    With zVM, you would still zone by WWN because the channels are configured for FCP but with a FICON channel, typically all ports are put into a single domain, index zone (not domain, port number). Since the host controls all I/O paths, there is no accidental discovery of things that don't belong to the host as might be the case in a Windows environment.

    In FICON environments, the typical approach is to stand up the fabric and leave it alone. You certainly could WWN zone, but this creates fabric maintenance problems in a FICON environment. A WWN belongs to a specific port connected to the fabric so if a customer where to upgrade a DASD (storage), the customer would have to update the zoning in the fabric as well. This is not something a FICON system programmer would normally think of doing. If a customer were to do a push-pull on a DASD controller, there is no additional work to be done.

    The only advantage WWN zoning would have is that WWN zones are small and the nature of a small WWN zone in a FICON environment is to limit the distribution of RSCNs. As with the fabric, hosts, DASD, tape, and CTCs are set up once and very infrequently changed so RSCNs are unusual. FICON ports simply discard RSCNs so there is no additional processing overhead associated with RSCNs.



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    Field Applications Engineer
    Broadcom
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  • 3.  RE: background of D,P (hard) zoning in case FICON

    Posted 11-07-2019 07:44 AM

    Thank you for your detailed reply @Jack Consoli​.

    What complicates our situation, is that the current DCX fabric serves mixed environment. It has distributed hosts, and zVM & z/OS as well. So the current zone database contains soft, and hard zoning too. As far as I know this is against best practice.
    Anyway, our short term plan is to migrate the MainFrame connections to other DCX-es, so we must change zoning anyway, we just would like to have a confirmation if the WWPN based zoning can be an option. From SAN admin perspective, this can be more easier to maintain/check.

    "You certainly could WWN zone, but this creates fabric maintenance problems in a FICON environment."

    The maintenance problem does mean that in case of storage extension/HBA failure, you should modify the zoning? ​

    Appreciate your reply.



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    Regards, Tamas.
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  • 4.  RE: background of D,P (hard) zoning in case FICON

    Posted 11-07-2019 08:21 AM
    Mixed Environment

    The term "soft zoning" in Brocade parlance means a mix of d,i and WWN zone members in the same zone. You definitely should not do that. Mixing zones that are all d,i with zones that are al WWN in the same zone configurations is fine and is not considered soft zoning.

    It is OK to mix FCP and FICON on the same switch. I'm assuming this in in production so to late to virtulaize the switch and keep them separate. The only time it makes sense to mix FCP and FICON is when the FCP is back end disk mirroring ports or zVM when the customer still wants to be able to use system automation tools or RMF on non-FICON ports.

    Maintenance Concern

    If a channel card (HBA) were to be replaced or a storage interface replaced due to a maintenance action, those ports would have new WWNs so you are correct, that is what would necessitate a zoning change. While that's just a normal operational change in the open space, FICON system programmers don't think of it and most have no idea what zoning is.

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    Field Applications Engineer
    Broadcom
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  • 5.  RE: background of D,P (hard) zoning in case FICON

    Posted 11-07-2019 09:51 AM

    Thank you for the enlightenment regarding "soft zoning". For me it wasn't 100% clear, and I mixed it with WWPN based zoning. The environment is in production state, so there is no such an option to do eg.: VirtualFabrics. We're supporting only the SAN from this solution, so any changes that requires zoning activities will land on our desk ...  hopefully in case of a HBA card replacement as well.

    Cheers.



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    Regards, Tamas.
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