[CentOS] Problem enabling write-back cache for IBM ServeRAID controller in CENTOS 4.2

Hi,

I have just upgraded an IBM Xseries x225 server to CentOS 4.2 (from 
CentOS 3.6) and found out that write back cache is not enabled for the 
drive representing the RAID array. The RAID controller has 128 MB 
battery backed cache. Write back cache is enabled in the controller 
configuration (using the IBM boot cd) and verified using the IBM 
RaidManager utility, but the boot messages show that the cache setup is 
write-through instead of write-back.

scsi0 : IBM PCI ServeRAID 7.10.18  Build 731 <ServeRAID 6i>
  Vendor: IBM       Model: SERVERAID         Rev: 1.00
  Type:   Direct-Access                      ANSI SCSI revision: 02
SCSI device sda: 213288960 512-byte hdwr sectors (109204 MB)
SCSI device sda: drive cache: write through
 sda: sda1 sda2

If I boot CentOS 3.6 in rescue mode I have write back cache enabled.
I have tried to use the sdparm utility to enable write back cache but it 
says that this parameter is not changeable.
 sdparm --get=WCE /dev/sda -6
    /dev/sda: IBM       SERVERAID         1.00
WCE        0  [Changeable: n, def: 0, saved: 0]

I have looked at the ips module parameters but none seem to affect the 
write cache. Any ideas how to enable write back cache?

Thanks,

Radu