[Gluster-devel] Testing SEEK_HOLE performance

[Christopher Pereira]

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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