File fragmentation on RAID-5 ? - Veritas Volume Manager

This is a discussion on File fragmentation on RAID-5 ? - Veritas Volume Manager ; Hi, to access data on two arrays we are using a database server called SPD from SAS. From our early performace tests we found that SPD-server can read data (in a clean-room environment) with about 120-150 MB/s. Now we are ...

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Thread: File fragmentation on RAID-5 ?

  1. File fragmentation on RAID-5 ?


    Hi,

    to access data on two arrays we are using a database server
    called SPD from SAS. From our early performace tests we found
    that SPD-server can read data (in a clean-room environment) with
    about 120-150 MB/s. Now we are down to 70 MB/s.

    I should mention that these rates can only be reached
    when the server has got a lot of threads running. If we read
    data in single-threaded mode we have got 7-8 MB/s per fs,
    whereas we had 15 MB/s earlier.
    I should mention as well that files on the RAID-5 are relatively
    large: 16-128 MB.

    The only difference I can see between the tests is that the
    disks in the arrays are now 80% filled, whereas with the first
    test only 40% were filled.

    So I'm wondering if the fragmentation of files can be the reason for
    the performace issue. Or is fragmentation not an real issue with
    RAID-5 and/or VVM?

    TIA
    ---
    Mathias


    Configuration:
    we are running VM 3.0.2 on Solaris 2.7 on two A5200
    (fibre-channel attached to E4500).
    Each array has got currently 6 RAID-5 ufs-fs.
    Each RAID-5 fs consists of 3 18GB disks.



  2. Re: File fragmentation on RAID-5 ?

    >>>>> "Mathias" == Mathias <" > writes:

    > So I'm wondering if the fragmentation of files can be the reason for
    > the performace issue. Or is fragmentation not an real issue with
    > RAID-5 and/or VVM?


    Fragmentation of files, and indeed files at all, is a phenomenon at
    filesystem level. RAID-5 and VxVM are things that live below
    the filesystem level. They can't have anything to do with file
    fragmentation even if they'd want to.
    --
    Calle Dybedahl, Vasav. 82, S-175 32 Jaerfaella,SWEDEN | calle@lysator.liu.se

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