Re: IO scheduler recommendation

Arni Kromić <arni.kromic@xxxxxxxxxxx> · Tue, 29 Jan 2019 09:05:54 +0100



    On 28/01/2019 14.15, Imre Samu wrote:

    
                  Phoronix website has some performance testing.
                  

                    for example:  (2018 Dec)  "Linux 4.20 I/O Scheduler
                    Benchmarks On NVMe SSD Storage"

                  
                  https://www.phoronix.com/scan.php?page=article&item=linux-420-io&num=3
                  "BFQ also picked up wins on the Samsung 970 EVO SSD
                  when running the PostgreSQL database server."
                  

                  (2017)"Linux 4.12 I/O Scheduler Benchmarks: BFQ,
                    Kyber, Etc"
                  https://www.phoronix.com/scan.php?page=article&item=linux-412-io&num=3

                  
                  "The default CFQ I/O scheduler on this SATA 3.0
                    SSD system remained the fastest for this PostgreSQL
                    benchmark."
                  

                  Imre
                  

        AB_ba# <bharti.anup@xxxxxxxxx>
          ezt írta (időpont: 2019. jan. 21., H, 12:05):

        
          Hello ,
            

            I searched the complete PostgreSQL Documentation but
              didn't get anything with respect to IO scheduler
              recommendation.
            What is being recommended by PostgreSQL ?
            Which is the best IO scheduler considering the Data is
              hosted on NFS?
            

              -- 

              Thanks
                and Regards

                ANUP BHARTI
            
          
    CFQ is supposed to be the best for servers anyway, because it is
    designed to ensure all services get fair (hence the name) amount of
    I/O transfer time, no matter what. Deadline is supposed to be better
    for interactive (e.g. desktop) use because it guarantees better
    response at the expense of overall throughput.

    
    The above mentioned schedulers are variants of the Elevator
    algorithm designed to optimize data handling on a rotating platter
    HDD with moving heads. NOOP scheduler, as its name sugests, does
    nothing. It is supposed to be best for devices which are NOT
    rotating platter, moving heads HDDs. Its case uses are SSDs which
    don't have mechanical movements to optimize, RAID controllers which
    themselves control their physical drives and VMs where the host OS
    is responsible for that.

    
    However all that is moot for NFS, which is used by the OP, for it is
    a network protocol, not a physical device. The question of
    schedulers is irrelevant because it CAN'T be set for NFS.

    -- 
Kind Regards,
Arni Kromić