Adaptec 2120S FreeBSD 4.11 poor performance

[Anton Turygin]

Goodafternoon.
I have a server with FreeBSD 4.11 inttalled.
I'm using an Adaptec 2120S with RAID 5 configured on it.

#uname -srm
FreeBSD 4.11-RELEASE-p4 i386
#aaccli
AAC0> controller details
Executing: controller details
Controller Information
----------------------
          Remote Computer: S
              Device Name: S
          Controller Type: No Info
              Access Mode: READ-WRITE
Controller Serial Number: Last Six Digits = C00DC3
          Number of Buses: 1
          Devices per Bus: 15
           Controller CPU: Unknown
     Controller CPU Speed: 100 Mhz
        Controller Memory: 64 Mbytes
            Battery State: Not Present

Component Revisions
-------------------
                 CLI: 1.0-0 (Build #5263)
                 API: 1.0-0 (Build #5263)
     Miniport Driver: 4.1-0 (Build #7244)
Controller Software: 4.1-0 (Build #7244)
     Controller BIOS: 4.1-0 (Build #7244)
Controller Firmware: (Build #7244)
Controller Hardware: 2.64

AAC0> disk list
Executing: disk list

C:ID:L  Device Type     Blocks    Bytes/Block Usage            Shared Rate
------  --------------  --------- ----------- ---------------- ------ ----
0:00:0   Disk            143374744 512         Initialized      NO     320
0:01:0   Disk            143374744 512         Initialized      NO     320
0:02:0   Disk            143374744 512         Initialized      NO     320

AAC0>



While:
#dd if=/dev/zero of=./file

#iostat -w 1 -d aacd0
            aacd0
   KB/t tps  MB/s
   0.00   0  0.00
   9.00   6  0.05
   9.00   6  0.05
  13.33   3  0.04
  32.20  89  2.80
  30.59 114  3.41
  44.46  69  2.98
  54.24  67  3.57
  47.08  96  4.43
  48.07  91  4.28
  54.02  93  4.92
  59.50  87  5.07
  57.01  86  4.77
  60.22  88  5.19
#


The speed in the array doesn't raise over 7 MB/s.
Can anyone help me to figure out?
Thanks in advance.


-- 
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RAZ-RIPE