Why fuse-sshfs performance is so poor?

fuse-sshfs performance is poor? It can only reach 10M/s over the gigabits-ethernet. On the both endpoint, ssh and sshd processes take the CPU usage less than 20% with a single core of Inteal-E5520. It seems the speed should be at least 40M/s.

]# dd if=olddata/diskdata count=100000 bs=64k skip=8000 | md5sum 316211200 bytes (316 MB) copied, 32.2354 seconds, 9.8 MB/s

]# dd if=olddata/diskdata count=100000 bs=4k skip=8000 | md5sum 28954624 bytes (29 MB) copied, 3.80448 seconds, 7.6 MB/s

]# dd if=olddata/diskdata count=100000 bs=512k skip=8000 | md5sum 30408704 bytes (30 MB) copied, 4.33369 seconds, 7.0 MB/s

Regards, Kirby Zhou from SOHU-RD +86-10-6277-8261