gvinum & raid5 on 8.0-RELEASE

[venom]

Hi, all.

I have problem with perfomance on raid5 volume.

***
AHCI mode enabled in BIOS settings
ahci.ko module is loaded

/8.0/-/RELEASE/ FreeBSD /8.0/-/RELEASE/ #0: Sat Nov 21 15:02:08 UTC 2009 
root at mason.cse.buffalo.edu:/usr/obj/usr/src/sys//GENERIC amd64/

# gpart show
=>   0  8192  md0  BSD  (4.0M)
      0    16       - free -  (8.0K)
     16  8176    1  !0  (4.0M)

=>   0  8192  ufsid/4b497774c23db769  BSD  (4.0M)
      0    16                          - free -  (8.0K)
     16  8176                       1  !0  (4.0M)

=>        34  1953525101  ada0  GPT  (932G)
           34         128     1  freebsd-boot  (64K)
          162  1953524973     2  freebsd-vinum  (932G)

=>        34  1953525101  ada1  GPT  (932G)
           34         128     1  freebsd-boot  (64K)
          162  1953524973     2  freebsd-vinum  (932G)

=>        34  1953525101  ada2  GPT  (932G)
           34         128     1  freebsd-boot  (64K)
          162  1953524973     2  freebsd-vinum  (932G)

=>        34  1953525101  ada3  GPT  (932G)
           34         128     1  freebsd-boot  (64K)
          162  1953524973     2  freebsd-vinum  (932G)


# gvinum printconfig

drive disk_3 device /dev/ada3p2
drive disk_2 device /dev/ada2p2
drive disk_1 device /dev/ada1p2
drive disk_0 device /dev/ada0p2
volume raid5
plex name raid5.p0 org raid5 512s vol raid5
sd name raid5.p0.s3 drive disk_3 len 1953524224s driveoffset 265s plex 
raid5.p0 plexoffset 1536s
sd name raid5.p0.s2 drive disk_2 len 1953524224s driveoffset 265s plex 
raid5.p0 plexoffset 1024s
sd name raid5.p0.s1 drive disk_1 len 1953524224s driveoffset 265s plex 
raid5.p0 plexoffset 512s
sd name raid5.p0.s0 drive disk_0 len 1953524224s driveoffset 265s plex 
raid5.p0 plexoffset 0s

# mount | grep raid5
/dev/gvinum/raid5 on /mnt/resc (ufs, local)

# cd /mnt/resc
# dd if=/dev/zero of=file count=16 bs=512k
16+0 records in
16+0 records out
8388608 bytes transferred in 44.871144 secs (186949 bytes/sec)


please, any solutions

--
Vladimir Ermakov