ZFS write speed

[S.N.Grigoriev]

Hi list,

I've got very low write speed using ZFS on a SATA disk.
My HDD configuration is:
ad4: 70911MB <WDC WD740BLFS-01YBU0 04.04V01> at ata2-master UDMA100 SATA 3Gb/s
ad6: 78532MB <Hitachi HDS728080PLA380 PF2OA60A> at ata3-master UDMA100 SATA 1.5Gb/s
ad8: 1430799MB <WDC WD15EARS-00MVWB0 51.0AB51> at ata4-master UDMA100 SATA 3Gb/s
ad4 and ad6 are single-slice disks (UFS2 with soft updates)

ZFS configuration is following:
zpool create Z ad8
zfs create Z/music
zfs create Z/video
All ZFS parameters are default.
kern.maxvnodes = 1000000

To test my configuration I recursively copied from ad6 to ad8 two directories.
The first one contains MP3 files (average size = 10MB).
The second one contains AVI files (average size = 1GB). 

To compare performance I repeated above tests with ad8 using UFS2 with soft updates.

18GB of MP3 files required 10m35s to copy to UFS2 and 21m40s to copy to ZFS.
30GB of AVI files required 16m6s to copy to UFS2 and 1h2m39s to copy to ZFS.

I used for tests FreeBSD 8.1R amd64. Amount of RAM on my machine is 6GB.

Any tips?

-- 
Regards,
Serguey.