Why so bad performance?

[kirbyzhou at sohu-rd.com (Kirby Zhou)]

I conustructed a 2-server/ 1 client gluster with Gigabit-ethernet, but got
so bad a benchmark.
Is there any thing can I tune?

[@65.64 ~]# for ((i=0;i<17;++i)) ; do dd if=/dev/zero of=/mnt/yyy$i bs=4M
count=2 ; done
2+0 records in
2+0 records out
8388608 bytes (8.4 MB) copied, 0.770213 seconds, 10.9 MB/s
2+0 records in
2+0 records out
8388608 bytes (8.4 MB) copied, 0.771131 seconds, 10.9 MB/s
...

[@123.21 glusterfs]# cat glusterfs-server.vol 
volume brick1
 type storage/posix 
 option directory /exports/disk1
end-volume

volume brick2
 type storage/posix 
 option directory /exports/disk2
end-volume

volume brick-ns
 type storage/posix
 option directory /exports/ns
end-volume

### Add network serving capability to above brick.
volume server
 type protocol/server
 option transport-type tcp/server     # For TCP/IP transport
 subvolumes brick1 brick2 brick-ns
 option auth.ip.brick1.allow 10.10.* # Allow access to "brick" volume
 option auth.ip.brick2.allow 10.10.* # Allow access to "brick" volume
 option auth.ip.brick-ns.allow 10.10.* # Allow access to "brick-ns" volume
end-volume

[@123.21 glusterfs]# cat glusterfs-client.vol 
volume remote-brick1_1
  type protocol/client
  option transport-type tcp/client
  option remote-host 10.10.123.21
  option remote-subvolume brick1
end-volume

volume remote-brick1_2
  type protocol/client
  option transport-type tcp/client
  option remote-host 10.10.123.21
  option remote-subvolume brick2
end-volume

volume remote-brick2_1
  type protocol/client
  option transport-type tcp/client
  option remote-host 10.10.123.22
  option remote-subvolume brick1
end-volume

volume remote-brick2_2
  type protocol/client
  option transport-type tcp/client
  option remote-host 10.10.123.22
  option remote-subvolume brick2
end-volume

volume brick-afr1_2
  type cluster/afr
  subvolumes remote-brick1_1 remote-brick2_2
end-volume

volume brick-afr2_1
  type cluster/afr
  subvolumes remote-brick1_2 remote-brick2_1
end-volume

volume remote-ns1
  type protocol/client
  option transport-type tcp/client
  option remote-host 10.10.123.21
  option remote-subvolume brick-ns
end-volume

volume remote-ns2
  type protocol/client
  option transport-type tcp/client
  option remote-host 10.10.123.22
  option remote-subvolume brick-ns
end-volume

volume ns-afr0
  type cluster/afr
  subvolumes remote-ns1 remote-ns2
end-volume

volume unify0
  type cluster/unify
  option scheduler alu
  option alu.limits.min-free-disk 10%
  option alu.order disk-usage
  option namespace ns-afr0
  subvolumes brick-afr1_2 brick-afr2_1
end-volume