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Optimizing FlashSystem / Storwize snapshots preferred paths

  • 1.  Optimizing FlashSystem / Storwize snapshots preferred paths

    Posted Tue June 15, 2021 10:33 AM
      |   view attached
    This week, I was working with one of my customer on a performance degradation. After looking at Storage Insight performance graphs and talking with support on a opened case, it was determined that it would be a good idea to optimize snapshots.
    Working with more and more customers that want to protect their data and ensure rapid recovery, we are seeing the adoption of snapshots and replication pickup at multiple customers. The use of softwares like IBM Spectrum Copy Data Management (CDM), IBM Copy Services Manager (CSM) is more and more common.

    Note that below, I refer to SVC, but this applies to Storwize v3700, v5000, v7000, v9000, FlashSystem 5000, 7000, 9000, and any Spectrum Virtualize based systems.

    When creating Flashcopy or Replication with change volumes, the Flashcopy volumes are used.
    When a Flashcopy is created, an FCmap between 2 volumes is created.
    The way Spectrum Virtualize functions is it will create each volume in a round robin manner.
    So in a 2 node cluster, volume 1 on node 1, volume 2 on node 2, volume 3 on node 1, volume 4 on node 2...
       This is the preferred path value of each volume.
    This allows the SVC to balance traffic and optimize performance on each SVC.
    But this design may not always optimize FlashCopies.
     
    Flashcopy is the process of taking 2 volumes and creating a map between them.
    The Flashcopy is a point in time of the volume.
    It just creates the map between the 2 volumes (source and target).
    There are cases where the 2 volumes will be on the same node preferred path, and other cases where it will not be.
    Having Flashcopy between volumes that are on different nodes is not optimal and will create more inter-node traffic.

    IBM has various tools that can create Flashcopy (point in time snapshots).
    IBM Spectrum Copy Data Management (CDM), IBM Copy Services Manager (CSM).
    But those tools are bound to the rules of SVC and as discussed above may not always optimize snapshot volume preferred paths.
    This is why I built this script that will look at all FCmaps.
    Pull the source volume preferred path and the target volume preferred path and compare them.
    If needed, the target volume will be changed to match the source volume.

    I thought this may be good for other customers and wanted to share the script.
    To run the script, copy and paste in SSH command line.
    To automate, you may want to look at tools like putty plink or other tools.
    You could also use the script with CDM and run as a post script that runs after a "backup" / snapshot job runs to ensure paths remain optimized.
     
    Here is the script
    See file "SVC Match FlashCopyPreferred vdisks.txt".

    ------------------------------
    Martin Gingras
    ------------------------------

    Attachment(s)



  • 2.  RE: Optimizing FlashSystem / Storwize snapshots preferred paths

    Posted Wed June 16, 2021 02:58 AM

    Hi,

     

    Thanks for responses, much appreciated.

     

    I stated LVM will be used for migration in the initial post so don't need any suggestions for alternative methods, but thanks anyway as always good to have input.

     

    I have answers I needed now and need to close this thread once I reset my password....again.

     

    John

     

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