[Bugs] [Bug 1220173] New: SEEK_HOLE support (optimization)

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1220173

            Bug ID: 1220173
           Summary: SEEK_HOLE support (optimization)
           Product: GlusterFS
           Version: pre-release
         Component: glusterd
          Severity: low
          Assignee: bugs at gluster.org
          Reporter: kripper at gmail.com
                CC: bugs at gluster.org, gluster-bugs at redhat.com



Gluster is currently not supporting SEEK_HOLE support which will boost
performance when working with sparse VM images.

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].

See also [2].

Setting to low prio, since it's an optimization.
Please feel free to change the prio according to the current project goals.

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

[2] http://thread.gmane.org/gmane.comp.file-systems.gluster.devel/10884

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