Gluster users - Jul 2015 - Read performances low compared to write

Hello,

I am evaluating GlusterFS and I have a question about read performance compared
to write performance.
Release is 3.6.3-1 on SLES 11 SP 3.
I have 12 storage nodes, configured in Ditributed-Replicated with 2 replicas.
Network is 10 Gb ethernet.
Filesystem used is xfs.

When I am doing a simple test with dd bs=1M count=102400 (100 GB file with
blocksize=1M), I have good perfs when writing:
  around 550 MB/s - 10 Gb network is the bottleneck (2 replicas)
but when reading, performances are less good: 470 MB/s
I read one replica and read performances on the node itself might be better
(around 800 MB/s)
I tried several parameters:
  performance.read-ahead: on
  performance.read-ahead-page-count: 16
  performance.io-thread-count: 32
  performance.cache-size: 1GB
I followed also performances hints for Linux kernel.

Has somebody hints to increase these read performances?

Thanks for your help!