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  • 1.  Best practices for MDisk count/layout with FlashSystem as SVC backend

    Posted Mon April 20, 2026 05:59 PM

    When using a FlashSystem as back-end storage for SVC, is there any best practice or guidance regarding the number and layout of MDisks within a pool?

    With IBM DS8000, I recall recommendations around always using an even number of MDisks across even/odd LSS to balance and optimize performance.

    I'm trying to understand if similar principles apply when the backend is IBM FlashSystem, or if the architecture (e.g., RAID layout, distributed resources, etc.) changes the approach.

    Specifically:

    • Is there an optimal or recommended number of MDisks per pool when using FlashSystem?
    • Can I place an odd number of mdisks on an mdiskgrp without any performance penalty?
    • Does balancing across internal structures (nodes/enclosures/IO groups) still matter in the same way?
    • Are there any real-world considerations (performance, rebuild behavior, queueing) that should influence MDisk design?

    Thanks and best regards.



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    SERGIO PARDOS
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  • 2.  RE: Best practices for MDisk count/layout with FlashSystem as SVC backend
    Best Answer

    Posted Tue April 21, 2026 02:08 AM
    Edited by SERGIO PARDOS Tue April 21, 2026 02:18 AM

    Hello Sergio,

    Have a look at Performance and Best Practices Guide for IBM Storage FlashSystem and IBM SAN Volume Controller

    Chapter 3.4.4

    For all-flash solutions, create 32 volumes from the available pool capacity, which can be reduced to 16 or even 8 for small arrays (for example, if you have 16 or fewer flash drives in a back-end pool).

    For FCM arrays, the number of volumes is also governed by load distribution. 32 volumes out of a pool with an FCM array is recommended.



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    Johanvan Arendonk
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  • 3.  RE: Best practices for MDisk count/layout with FlashSystem as SVC backend

    Posted Tue April 21, 2026 02:19 AM

    Thanks, Johanvan 

    I assume the guidance above applies to the FlashSystem side. Now, once those (ie) 32 volumes are created and mapped to the SVC, let's assume I need to have several pools for organizational purposes... is there any specific guidance in regard of the number of managed disks I assign to each one of these mdiskgroups? 

    Thanks again and best regards.



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    SERGIO PARDOS
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    Original Message


  • 4.  RE: Best practices for MDisk count/layout with FlashSystem as SVC backend

    Posted Tue April 21, 2026 02:47 AM

    Sergio,

    As far as I know, there are no specific recommendations regarding the number of mdisks per pool (except that there is a restriction on the maximum number of mdisks per pool).
    Personally, I would use more than 1 in this case.  You could also consider using childpools.


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    Johanvan Arendonk
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    Original Message


  • 5.  RE: Best practices for MDisk count/layout with FlashSystem as SVC backend

    Posted Tue April 21, 2026 08:35 AM

    Thanks, Johan.



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    SERGIO PARDOS
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    Original Message


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