Testing SEEK_HOLE performance

Christopher Pereira <kripper@xxxxxxxxxxxx> · Sat, 09 May 2015 05:50:56 -0300



    Hi,

    
    I did a local sparse image copy benchmark copying from a gluster
    mount (of a local gluster-server) vs copying directly from the
    gluster-brick to test SEEK_HOLE support and performance.

    Motivation : VM's image files are sparse.

    Benchmark:

    cp /mnt/gluster-mount/image to /tmp/

      => takes 1m31.586s

      
      cp /mnt/ext4/gluster-brick/image to /tmp/

      => takes 0m29.215s (3 times faster!)

    
    Target: sparse qcow2 image file

    
    logic size: 30G

    physic size: 1.9G

    
    Commands like 'cp' call lseek(NEXT_HOLE) and lssek(SEEK_DATA) to
    skip useless zeros on modern filesystems [1].

    Is this supported on the gluster client? Is the server sending some
    kind of holes-index-buffer to the client?

    
    [1] lseek & SEEK_HOLE: http://linux.die.net/man/2/lseek

    
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