[rhn-users] LSI MegaRAID and "write-back" mode with battery backup

[Eric Pearce]

Has anyone out there got the combination of a LSI MegaRAID 320-1 and the 
battery module LSIBBU01 to perform in the "write-back" mode instead of 
"write-through" ?   This is Redhat ES 4.0 with 2.6.9-11.ELsmp x86_64.   I've 
confirmed that the battery is seen by the controller and fully charged. 
I've read that there should be a substantial performance improvement using 
"write back".  Hardware is a SuperMicro 6014P-82RB with dual 3.8Ghz Xeon + 
16Gb RAM, 15Krpm Seagate disks.
The MegaRAID BIOS is configured for "write-back" for each logical drive, but 
dmesg reports using "write through" as seen below...does this mean that 
write-back is not enabled?  Or is this functionality not visible to Linux?
Thanks
-e

megaraid cmm: 2.20.2.5 (Release Date: Fri Jan 21 00:01:03 EST 2005)
megaraid: 2.20.4.5 (Release Date: Thu Feb 03 12:27:22 EST 2005)
megaraid: probe new device 0x1000:0x1960:0x1000:0x0520: bus 2:slot 1:fun
c 0
ACPI: PCI interrupt 0000:02:01.0[A] -> GSI 24 (level, low) -> IRQ 209
megaraid: fw version:[1L37] bios version:[G119]
scsi2 : LSI Logic MegaRAID driver
scsi[2]: scanning scsi channel 0 [Phy 0] for non-raid devices
  Vendor: SUPER     Model: GEM318            Rev: 0
  Type:   Processor                          ANSI SCSI revision: 02
scsi[2]: scanning scsi channel 1 [virtual] for logical drives
  Vendor: MegaRAID  Model: LD0 RAID1 34731R  Rev: 1L37
  Type:   Direct-Access                      ANSI SCSI revision: 02
SCSI device sda: 71129088 512-byte hdwr sectors (36418 MB)
sda: asking for cache data failed
sda: assuming drive cache: write through
 sda: sda1 sda2 sda3
Attached scsi disk sda at scsi2, channel 1, id 0, lun 0
  Vendor: MegaRAID  Model: LD1 RAID1 40013R  Rev: 1L37
  Type:   Direct-Access                      ANSI SCSI revision: 02
SCSI device sdb: 286746624 512-byte hdwr sectors (146814 MB)
sdb: asking for cache data failed
sdb: assuming drive cache: write through
 sdb: sdb1 sdb2 sdb3 sdb4 < sdb5 >
Attached scsi disk sdb at scsi2, channel 1, id 1, lun 0