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how to control hdisk preference with lv scheduling policy

  • 1.  how to control hdisk preference with lv scheduling policy

    Posted Fri November 06, 2009 04:24 AM

    Originally posted by: j.gann


    Hi all,

    we mirror lvs across 2 storage systems (local, remote). remote storage has less io throughput than local. with the default lv scheduling policy lvm will write in parallel and read form the "first" disk until its 100% busy and then use the "second" mirrored disk. so for writing, the remote disk throughput limits the overall mirror IO performance. no luck there.
    for reading I like to make sure that the first disk chosen is a local one. iostat shows one of the disks of a mirror getting far more reads than the other one.
    does anyone know how the "first" disk in this algorithm is chosen? from iostat I suspect that the lower hdisk# will be used as first disk and this disk will do the majority of read IO.
    i would like to control this to make a disk from local storage always the first one chosen for reads.

    Any input welcome
    Joachim
    #AIX-Forum


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