S2600 single controller abnormal make write back to write through

Virtual host copy documents from S2600 to FujitsuDX400, too slow, IO speed is about 1.2Mb/s.
User condition:
Storage system: Huawei S2600
Third party storage: FujitsuDX400
Host system: Windows 2003，VMWare ESX
Topo structure:

none

 Configure lun to force write back through ISM.
OceanStor: admin> showlun -i 0
    =====================================================================
                               LUN Information
    ---------------------------------------------------------------------
     ID                            |  0
     Name                          |  Lun000_Vmware-0
     Status                        |  Normal
     Capacity(MB)                  |  1048576
     Stripe Unit Size(KB)          |  64
     RAID Group ID                 |  0
     Format Progress(%)            |  --
     Ascription Controller         |  A
     Working Controller            |  A
     Cache Prefetch Strategy       |  Intelligent
     Cache Write Strategy          |  Write back mandatory; No mirroring
     Running Cache Write Strategy  |  Write back; No mirroring
     Extendable Capacity(MB)       |  0
     Extended Capacity(MB)         |  0
    =====================================================================

Login on storage through cli and check S2600 log information
OceanStor: admin> showsys
=====================================================
                               System Information
---------------------------------------------------------
     System Name           | 
     Device Model          |  OceanStor S2600
     Current System Mode   |  Single Controller Fault
     Location              |
     System Time           |  2011-05-24 15:31:04
     Device Serial Number  |  210231G324Z097000004
     Product Version       |  V100R001C02
     iSCSI Device Name     |  iqn.2006-08.com.huawei:oceanstor:21000022a100d
                           |  031:notconfig
=====================================================
OceanStor: admin> showlun -i 0
==============================================================
                            LUN Information
--------------------------------------------------------------
     ID                            |  0
     Name                          |  Lun000_Vmware-0
     Status                        |  Normal
     Capacity(MB)                  |  1048576
     Stripe Unit Size(KB)          |  64
     RAID Group ID                 |  0
     Format Progress(%)            |  --
     Ascription Controller         |  A
     Working Controller            |  A
     Cache Prefetch Strategy       |  Intelligent
     Cache Write Strategy          |  Write back; No mirroring
     Running Cache Write Strategy  |  Write through; No mirroring
     Extendable Capacity(MB)       |  0
     Extended Capacity(MB)         |  0
==============================================================
System information is abnormal, single controller fault.
Lun configuration is abnormal, lun configuration is write back, function is write through.
  This S2600 is old version single controller storage, it has no BBU. It should be PDU, but in fact user does not configure PDU.
Then S2600 lose part of battery , when setting LUN cache to write back, S2600 can not find battery protection, so in order to protect data , it modify cache to write through , IO capability declines seriously.

Face to old S2600 single controller ,you need to configure lun to  force write back