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  • 1.  Storage Virtualize number of paths

    Posted Sun May 28, 2023 06:04 AM

    Hello All, 

    In IBM Redbook Performance and Best Practices Guide for IBM Spectrum Virtualize 8.5  is stated:

    Chapter 2.4.5 Host Zones
    Note: Eight paths per volume are supported. However, this design provides no
    performance benefits and in some circumstances can reduce performance. Also, it does
    not significantly improve reliability nor availability. However, fewer than four paths do not
    satisfy the minimum redundancy, resiliency, and performance requirements.

    Chapter 8.1.1 Number of paths

    As a best practice, limit the total number of FC paths per volume to four. For HyperSwap and
    stretched cluster configurations, eight paths per volume are recommended. Adding paths
    does not significantly increase redundancy, and it tends to bog down the host with path
    management. Also, too many paths might increase the failover time.

    No I would like to understand why eight paths for a Hyperswap and Stretched Cluster configuration?

    Thanks!



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    TMasteen
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  • 2.  RE: Storage Virtualize number of paths

    Posted Mon May 29, 2023 01:16 AM

    With either HS or SC, you have two systems, ergo each system should have 4 paths, so 4+4, yields the 8 paths for HS/SC configurations, ensuring each cluster set of nodes have 4 paths, each, without too much further Host path management.



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    ANDREW GREENFIELD
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    Original Message


  • 3.  RE: Storage Virtualize number of paths

    Posted Mon May 29, 2023 02:20 AM
    Hello Andrew,

    Thanks for reply.
    I'm not sure what you mean with two systems?
    In a stretched cluster the IOgroups are like in a normal SVC cluster in 1 system (Cluster) and the nodes of these IOgroups are just stretched over two Sites.
    A VDisk is "belonging" to 1 IOgroup (just like a normal SVC cluster) and the host is zoned to that IOgroup.

    So I still dont see the difference in recommendation between 4 and 8 paths.



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    T Masteen
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    Original Message


  • 4.  RE: Storage Virtualize number of paths

    IBM Champion
    Posted Mon May 29, 2023 03:01 AM
    Edited by Nezih Boyacioglu Mon May 29, 2023 03:02 AM

    As a writer of this chapter in the IBM Redbook, I totally agree with Andrew. In a Hyperswap environment, you have two FlashSystems, and your logical volume has two physical copies. if your host zoned with those two FlashSystems your host's single port is zoned with each of the 4 controllers, and two ports become 8 paths.



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    Nezih Boyacioglu
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    Original Message


  • 5.  RE: Storage Virtualize number of paths

    Posted Mon May 29, 2023 03:48 AM
    Edited by T Masteen Mon May 29, 2023 04:03 AM
    Hello Nezih,
     
    With Flashsystems we cannot have a Stretched Cluster (as we can with SVC), and in the Redbook is stated:
    As a best practice, limit the total number of FC paths per volume to four. For HyperSwap and stretched cluster configurations, eight paths per volume are recommended. 
     
    So I wondered if I was missing something?
     
    Thanks,



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    T Masteen
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    Original Message


  • 6.  RE: Storage Virtualize number of paths

    IBM Champion
    Posted Mon May 29, 2023 04:09 AM
    is this your connection scheme?



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    Nezih Boyacioglu
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    Original Message


  • 7.  RE: Storage Virtualize number of paths

    Posted Mon May 29, 2023 04:22 AM

    No, we have a Stretched Cluster with 6x SV2 Nodes

    SVC Stretched Cluster


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    T Masteen
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    Original Message


  • 8.  RE: Storage Virtualize number of paths

    IBM Champion
    Posted Mon May 29, 2023 04:33 AM

    if your hosts cannot access the site2 as shown, your paths would be 4. 
    if your hosts access the site2 your paths would be 8. 
    it's a design decision, how your hosts will continue to access your data during controller based and/or site based failures. 
    There are many customers whose hosts have connections to site2 controllers. Then they have 8 paths. 



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    Nezih Boyacioglu
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    Original Message


  • 9.  RE: Storage Virtualize number of paths

    IBM Champion
    Posted Fri June 02, 2023 05:30 AM

    So no matter how many nodes a SVC cluster has, the host and its volumes should always be zoned against only one IO group and its NPIV paths. Two physical connections per switch and node, preferably distributed over two adapters, resulting in a total of eight paths per volume, four of which are not preferred. 
    The preferred paths should be the only ones used in a clean multi-pathing configuration.

    Please have a look at the following blog from Barry:

    https://barrywhytestorage.blog/2020/10/28/lets-get-this-right-once-and-for-all-alua-passive-active-active-is-not-precluded-by-alua/

    In a stretched cluster or HyperSwap environment, site id's are assigned for the controllers, storage systems and hosts. 
    These control the preffered and non-preffered paths. Servers via SCSI and ALUA get the controllers on the same side assigned as preffered and the remote side as non-preffered.

    Together with NPIV takeover it is ensured that in case of node failure the paths on the remaining nodes of the same IO group can be taken over and this happens without effects on the multipathing of the host.

    Finally the question arises why in a clean NPIV environment, with site id's, the remote side is visible at all, probably only as a safeguard.



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    Patrik Groß
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    Original Message