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IJ53188: IO PERFORMANCE IS DEGRADED ON REDHAT 9

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APAR status

  • Closed as program error.

Error description

  • After updating NSD servers as example from RHEL 8.6 to
RHEL9.4 (kernel 5.14.0-427.20.1.el9_4.x86_64) there is a
degraded IO performance seen.
Investigation revealed that this due to  upstream kernel
commit:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
linux.git/commit/?id=eded341c085b
"block: don't decrement nr_phys_segments for physically
contigous segments" in combination with how Storage Scale
is setting up bvecs in cxiIOBuffer.c in
the GPFS kernel module. The above commit changes the
kernel behavior so it removes coalescence "optimization
under the assumption that most users already
build good enough bvecs".


Reported in: 5.1.9

Local fix

  • 



Problem summary


    

  • Disk I/O performance improvement necessary after Linux kernel
changes.

    



Problem conclusion


    

  • A Linux kernel change caused GPFS to break disk I/O into many
small requests.

    



Temporary fix


    

  • 



Comments


    

  • 



APAR Information




    

  • APAR number
    IJ53188
    • 

  • Reported component name
    SPEC SCALE DME
    • 

  • Reported component ID
    5737F34AP
    • 

  • Reported release
    519
    • 

  • Status
    CLOSED  PER
    • 

  • PE
    NoPE
    • 

  • HIPER
    NoHIPER
    • 

  • Special Attention
    NoSpecatt / Xsystem
    • 

  • Submitted date
    2024-12-16
    • 

  • Closed date
    2026-05-07
    • 

  • Last modified date
    2026-05-07
    • 





    

  • APAR is sysrouted FROM one or more of the following:
    

    • 

  • APAR is sysrouted TO one or more of the following:
    

    • 



Fix information


    

  • Fixed component name
    SPEC SCALE DME
    • 

  • Fixed component ID
    5737F34AP
    • 



Applicable component levels


    








      
              
                            

              

              [{"Business Unit":{"code":"BU048","label":"IBM Software"},"Product":{"code":"STXKQY"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"519","Line of Business":{"code":"LOB69","label":"Storage TPS"}}]
              

                                                                    

          
 
        

      

    

      

        

          

            
Document Information


            

            


                        

            Modified date:
            

            07 May 2026
            

            
                      

        


        

        


      

    

  



    

  

  
    
            

          
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