Gluster users - Mar 2012 - Gluster-users Digest, Vol 47, Issue 10, topic 1, write perf.

Harold Hannelius, 

If you are using the "cp" utility to copy into Gluster then you may be
running into a problem with use of an extremely small record size coupled with
write replication overhead, try
dd if=/dev/zero of=/gluster/test.dd bs=1024k count=256
Which uses a 1-MB write size, and see if that behaves differently.
I'm not a debian expert but in RHEL5.3 the "cp" utility record
size was 4 KB and in RHEL6.2 the same utility has a 32-KB I/O size, you can
check using strace utility.
For small-write-size utilities you can also try NFS to Gluster server, since NFS
client aggregates writes.