enable disk cache on SAS 6/iR ?

Hi all,

 

Just got 2 Dell PowerEdge 1950 (8GB RAM each, SAS 6/iR controller: LSISAS1068E, FwRev=00142e00).  The only difference is disk:
machine A: 2 x 146GB (15000rpm, RAID 1, Model: ST3146855SS       Rev: S527)
machine B: 2 x 500GB (7200rpm, RAID 1, Model: ST3500630NS       Rev: 3BKS)

Both systems show that disk cache is set to 'write back' after raidcfg tool shows following setting on both systems:

 

Read cache: no read ahead

Write cache: write through

Disk cache: no applicable (or something like that)

 

Even more strange is that when we run load test tool for BerkeleyDB that requires sync to disk upon transaction commit, machine B is much faster than machine A (almost double or triple the performance).

 

Since only the disks are difference, I wonder if it relates to some settings for different SAS 6/iR+disk combination.  Would anyone please help?

 

Thanks a lot.

/ST Wong