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  • 1.  Max LUN size with Oracle

    Posted 11/05/25 01:01 PM

    Section 5.9.1 of Redbook "Oracle on IBM Power Systems" (sg248485) recommends to limit LUNs to 512 GB.  Is that recommendation still considered current?

    Trying to spec a new LPAR for oracle database server installation, and the database is currently 16TB in size.

    Keeping with the multiple of 8 for # of LUNS, start with 48 LUNS that are 400GB, and every few years ask SAN team to expand the LUNS by 50GB, to accommodate for growth?



    ------------------------------
    Gerald Stephens
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  • 2.  RE: Max LUN size with Oracle

    Posted 11/05/25 01:41 PM
    On Wed, Nov 05, 2025 at 06:00:48PM +0000, Gerald Stephens via IBM TechXchange Community wrote:
    > Section 5.9.1 of Redbook "Oracle on IBM Power Systems" (sg248485)
    > recommends to limit LUNs to 512 GB. Is that recommendation still
    > considered current?

    That does sound really small. I use 1T or 2T LUNs, because I want at
    least 4 LUNs in any VG for interdisk PP striping. If you have growth,
    always add another 4 LUNs minimum to avoid hot LUNs.

    Why not use 16 x 1T LUNs, and a scalable VG? You can add 4 x 1T for
    growth each year with reasonable balance and not have to do a reorgvg.

    I'd also suggest using multiple filesystems in the VG. Don't have a
    filesystem that would take longer to fsck than you can handle
    downtime. For instance, you might have your 16TB VG, but make each
    JFS2 filesystem 4TB (ie: /u01-/u04). If you have to fsck, you can run
    4 FS in parallel.

    Be sure to doublecheck your hdisk attributes to enable active/active
    pathing, which may need no_reserve set. Increase your queue depth as
    well.

    Good luck!

    ------------------------------------------------------------------
    Russell Adams Russell.Adams@AdamsSystems.nl
    Principal Consultant Adams Systems Consultancy
    https://adamssystems.nl/




  • 3.  RE: Max LUN size with Oracle

    Posted 11/06/25 01:15 AM

    Dear Gerald, 

    regarding the LUN limit , you have to consider a lot of limitation that control the LUN size, ex:

    if there is oracle data guard or if there is a storage replication as well as it depends on the storage brand and replication way. all of theses information need to know from each team before you take the LUN size decision.

    From my experience working in OS and storage department together to support and work with database teams, usually the LUN size is smaller or equal 2 TB. 



    ------------------------------
    Hashem Al-Qaisi
    Senior Systems Engineer
    Jordan Business Systems
    ------------------------------



  • 4.  RE: Max LUN size with Oracle

    Posted 11/06/25 04:13 AM

    Hi

    if you asking for LUN size on AIX it self ,the maximum LUN size on AIX is limited by the storage subsystem and the AIX version, with specific limits potentially , please check below IBM link for limitations for logical storage management 

    https://www.ibm.com/docs/en/aix/7.3.0?topic=concepts-limitations-logical-storage-management


    but for Oracle DB lun size i think better to check the recommendations from Oracle it self ,    Oracle databases on AIX you have to consider both performance and manageability and it's ASM ?

    so better the recommendation for Oracle LUN to provide from DBA

    Thanks



    ------------------------------
    Anas AlSaleh
    IBM Power Systems Software Specialist
    Saudi Business Machines ( SBM )
    Riyadh
    ------------------------------



  • 5.  RE: Max LUN size with Oracle

    Posted 11/06/25 11:09 AM

    With older Oracle releases < 12.1 the ASM maximum LUN size was 2TB, so the 512GB was a "starting point" to allow for significant growth - SAN based LUN size increase - without having to add more LUNs.

    How much growth do you expect? What are the IO characteristics?

    The "number of LUNs" you work with is driven by several factors - not just size. After you determine the number of LUNs you will need then you can size the LUNs according to your required space requirements.

    I suggest you review the related material in the 2024 VUG session which provides some additional discussion on what to look out for re AIX and IO layout for Oracle databases.

    https://www.ibm.com/support/pages/ibm-power-virtual-user-group  and then search for the Oracle on AIX - Best Practices sessions May, 2 and May, 7 from 2024.



    ------------------------------
    Ralf Schmidt-Dannert
    ------------------------------



  • 6.  RE: Max LUN size with Oracle

    Posted 11/07/25 07:56 AM

    Lots of great info, thanks.  Ralf - thanks for the links to the Power VUG content!

    A little more background on our system....

    We are migrating from AIX 7.2 / oracle 11g to AIX 7.3 with Oracle 19c

    I only have access to the LPAR.  SAN / power hardware and VIOS are maintained by another govt department.  SAN is hitachi.  I implement the disk tuning parameters supplied from the team installs the power HW and build the VIOS.  Largest LUN on AIX is currently 8TB , we do have LUNS on windows servers from same SAN that are 32 TB, general preference is not to exceed 8TB, as directed by SAN team.

    We are using bigfile tablespace, and the largest single dbf is approx 7TB, and total db is approx 11 TB.  We expect 1.5-2.0 T of growth a year.  DBAs are reviewing the choice of bigfile tablespace.....

    During business hours, all run fine, but we see that our RMAN backups are running into business hours, and the bottleneck is disk.  

    at this point, best to start the build, test, and revise as needed, and then prep for production move.  Lots of moving balls here....



    ------------------------------
    Gerald Stephens
    ------------------------------

    Original Message


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