Poor performance on 10 Gbps SAN

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Hi,

I'm in the process of building a 10 Gbps Ethernet SAN and would really like to use AoE, but I'm experiencing poor performance (320 MB/s sequential reads and writes). The access pattern on this SAN will be almost exclusively sequential so I am interested in maximizing throughput, not IOPS.

The status quo:
* RAID 60 (1 MB stripe size) on target capable of 900 MB/s write and 1400 MB/s read on ext4 (sequential).
* Jumbo frames (9000) configured and working on target, initiator and Dell PowerConnect 8132 switch (with hardware flow control enabled).
* iperf benchmarks TCP performance at 9.87 Gb/s.
* aoetools-36, vblade-21 and kernel 3.10.7 with AoE v81

I'm using the following tuning parameters as suggested on this list:
net.core.rmem_default = 278528
net.core.rmem_max = 278528
net.core.wmem_default = 278528
net.core.wmem_max = 278528
net.core.netdev_max_backlog = 10000

I exported the RAID 60 as e0.0. Both read and write performance is disappointing, though:

# dd if=/dev/etherd/e0.0 of=/dev/null bs=1M count=4K
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 15.9536 s, 269 MB/s

# dd if=/dev/zero of=/dev/etherd/e0.0 bs=1M count=4K conv=fdatasync
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 13.6141 s, 315 MB/s

Read speed is even worse than write, which is odd. To rule out any doubts about RAID performance I exported a 4 GB ramdisk as e0.1, but the results are just as bad:

# dd if=/dev/etherd/e0.1 of=/dev/null bs=1M count=4K
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 15.1406 s, 284 MB/s

# dd if=/dev/zero of=/dev/etherd/e0.1 bs=1M count=4K conv=fdatasync
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB) copied, 13.3615 s, 321 MB/s

dd, vblade and the aoe kernel threads are well below 100% CPU usage during these tests. What am I missing here?

Thanks in advance,
Derick
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