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