zfs generate a lot of IO ?

hi,
I install CURRENT with zfs root fs on my notebook(T60P). GENERIC
configuration
without INVARIANTS and WITNESS.
I run a program to test. This program basically read a few small files
and calcuate and output a small file.
On FreeBSD6.2, iostat show that It generate a few io operation.
But on zfs, generate a lot:

# lsof -p 10441
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
hyposat 10441 root cwd VDIR 0,145 512 2 ()
hyposat 10441 root rtd unknown file system type: zfs
hyposat 10441 root 0u VCHR 0,150 0t15080 147 ()
hyposat 10441 root 1u VCHR 0,150 0t15080 147 ()
hyposat 10441 root 2u VCHR 0,150 0t15080 147 ()
hyposat 10441 root 3u unknown file system type: zfs
hyposat 10441 root 4u VREG 0,145 8605 11 -- hyposat-out

#iostat 1
tty ad4 da0 pass0 cpu
tin tout KB/t tps MB/s KB/t tps MB/s KB/t tps MB/s us ni sy in id
10 634 126.65 170 21.00 0.00 0 0.00 0.00 0 0.00 16 0 36 0 48
3 295 127.17 275 34.12 0.00 0 0.00 0.00 0 0.00 15 0 28 1 56
7 571 128.00 361 45.08 0.00 0 0.00 0.00 0 0.00 15 0 17 0 68
3 621 126.51 154 19.01 0.00 0 0.00 0.00 0 0.00 14 0 33 1 53
10 154 126.97 223 27.62 0.00 0 0.00 0.00 0 0.00 12 0 31 0 56
344 558 128.00 375 46.83 0.00 0 0.00 0.00 0 0.00 16 0 18 0 67
72 78 128.00 466 58.19 0.00 0 0.00 0.00 0 0.00 14 0 10 1 76
344 78 128.00 437 54.57 0.00 0 0.00 0.00 0 0.00 16 0 9 0 75
7 91 128.00 475 59.32 0.00 0 0.00 0.00 0 0.00 12 0 13 0 75
43 621 126.63 168 20.75 0.00 0 0.00 0.00 0 0.00 15 0 31 0 53
24 78 128.00 479 59.82 0.00 0 0.00 0.00 0 0.00 14 0 14 1 72
200 78 128.00 476 59.44 0.00 0 0.00 0.00 0 0.00 11 0 12 0 76
384 78 128.00 473 59.07 0.00 0 0.00 0.00 0 0.00 12 0 14 0 74
264 78 128.00 450 56.19 0.00 0 0.00 0.00 0 0.00 17 0 12 1 71
0 78 128.00 463 57.82 0.00 0 0.00 0.00 0 0.00 13 0 11 2 74
0 78 128.00 464 57.94 0.00 0 0.00 0.00 0 0.00 14 0 14 1 71
0 306 127.82 407 50.75 0.00 0 0.00 0.00 0 0.00 17 0 13 0 70
0 78 0.00 0 0.00 0.00 0 0.00 0.00 0 0.00 2 0 0 0 98
0 77 0.00 0 0.00 0.00 0 0.00 0.00 0 0.00 3 0 0 0 97
0 77 34.00 4 0.13 0.00 0 0.00 0.00 0 0.00 5 0 2 0 94
tty ad4 da0 pass0 cpu

The output file "hyposat-out" is really small(<8kb), program "hyposat"
is also
small(<7MB). Something wrong on my configuration?

--hwh