Global Storage

Global Storage Forum

Connect, collaborate, and stay informed with insights from across Storage

 View Only

  • 1.  Luns size for IBM i

    Posted Wed August 23, 2023 02:42 PM

    Some time I was told that there is a type of disk where they recommend creating larger LUNs, so that their performance would work better, but I don't remember what type of disk it is, on the other hand the storage performance manual regarding LUNs for IBM i asks LUN less than 200 GB, what do you recommend me to do? make 300 GB LUNs?



    ------------------------------
    Miguel Peralta
    ------------------------------


  • 2.  RE: Luns size for IBM i

    Posted Thu August 24, 2023 02:15 AM

    Dear Miguel

    There are some facts to consider. 1st : IBM i did not use the classic 512 Bytes per Block, they are using 520 Bytes. This is related to the fact, that IBM I did not separate RAM from Disk, they have one Storagespace.

    2nd: IBM I uses Queues to communicate to the disks and the more disks you have, the more queues you have, that will increase IBM I Performance.

    3rd : Don´t mix up GB and GiB. GB is a decimal number (1000*1000*1000) and the GiB are binary (1024x1024x1024). The difference is 6,9% at Gigabyte

    I will sugest, that you read the IBM Redbook Performance and Best Practices Guide for IBM Storage FlashSystem and IBM SAN Volume Controller (for IBM Storage Virtualize 8.6)

    kind regards Martin



    ------------------------------
    Martin Haussmann
    SE
    TD SYNNEX
    ------------------------------

    Original Message


  • 3.  RE: Luns size for IBM i

    Posted Fri September 01, 2023 08:41 AM

    Miguel

    You may confuse between disk unit size and disk controller card's cache size from the time of HDD.    For Power Systems, there are several types of SAS disk controller card to buy. For IBM i, it is always recommended to use one with the LARGEST CACHE SIZE (I think it was some 7 GB compresses on 2 GB physical size).   This fact still stands for internal SSD as well but it is less compelling since the time of POWER9 HW.

    For IBM i using SAN SSD/FlashDisk, you should NOT care about LUN size. What is more important is the total number of LUNs.  I use a rule-of-thumb that you need at lease 4 LUNs per core for low to medium workload, 8 LUNS per core for high workload, but the more the better in general.   Do not use this rule for the case of internal HDD. You need 100% more for this case. 



    ------------------------------
    Chance favors only the prepared mind.
    -- Louis Pasteur
    ------------------------------
    Satid S.
    ------------------------------

    Original Message


Related Content