EXT4 is ~2X as slow as XFS (593MB/s vs 304MB/s) for writes?

[Justin Piszcz <jpiszcz@lucidpixels.com>]

Hello,

Is it possible to 'optimize' ext4 so it is as fast as XFS for writes?
I see about half the performance as XFS for sequential writes.

I have checked the doc and tried several options, a few of which are shown
below (I have also tried the commit/journal_async/etc options but none of 
them get the write speeds anywhere near XFS)?

Sure 'dd' is not a real benchmark, etc, etc, but with 10Gbps between 2 
hosts I get 550MiB/s+ on reads from EXT4 but only 100-200MiB/s write.

When it was XFS I used to get 400-600MiB/s for writes for the same RAID 
volume.

How do I 'speed' up ext4?  Is it possible?

raid0_11 disks: (XFS)
# /dev/md0        /r1             xfs     noatime         0       1
p63:/r1# dd if=/dev/zero of=bigfile1 bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 18.1021 s, 593 MB/s
p63:/r1#

raid0_11 disks: (EXT4)
# /dev/md0        /r1             ext4     noatime         0       1
# dd if=/dev/zero of=file bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 35.3741 s, 304 MB/s
p63:/r1#

Other tests (ext4)
p63:~# mount /dev/md0 /r1 -o data=writeback
p63:~# cd /r1
p63:/r1# dd if=/dev/zero of=file bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 39.8746 s, 269 MB/s
p63:/r1#

p63:~# mount /dev/md0 /r1 -o data=writeback,nobarrier
p63:/r1# dd if=/dev/zero of=file bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 40.0656 s, 268 MB/s

Justin.