I/O problems

[Brad Scalio]

Greetings,

We have DL380G6 servers with a RAID configuration as follows:

Smart Array P410i in Slot 0

   Bus Interface: PCI

   Slot: 0

   Serial Number: 5001438008F7C420

   Cache Serial Number: PACCQ0E9VYQ05QX

   RAID 6 (ADG) Status: Disabled

   Controller Status: OK

   Chassis Slot: 

   Hardware Revision: Rev C

   Firmware Version: 3.00

   Rebuild Priority: Medium

   Expand Priority: Medium

   Surface Scan Delay: 3 secs

   Queue Depth: Automatic

   Monitor and Performance Delay: 60 min

   Elevator Sort: Enabled

   Degraded Performance Optimization: Disabled

   Inconsistency Repair Policy: Disabled

   Post Prompt Timeout: 15 secs

   Cache Board Present: True

   Cache Status: OK

   Accelerator Ratio: 100% Read / 0% Write

   Drive Write Cache: Enabled

   Total Cache Size: 256 MB

   Battery Pack Count: 0

   SATA NCQ Supported: True

My question is this ... first off, we enabled Drive Write Cache due to postGreSQL logging causing heavy I/O and disk wait at times of heavy loads.  But, the Accelerator Ratio is obviosuly set to maximize reads.  Since we don't have a BBWC (Pack Count - 0) - and yes we know that means the cache is lost on reboot or power outage - the questions is:

[1] Does the accelerator ratio matter?  Should it be 25/75 or 0/100 if we are only doing key scan reads.

[2] Can we not change the cacheratio with hpacucli or for that matter any RAID parameters without a BBWC battery.

I was debating there possibly being an issue with I/O reordering, using the CFQ scheduler, and a write cache, does the controller re-order writes again if the CFQ reorders them during times of heavy I/O?  Or, does this really even matter much since we are only mirroring two disks in RAID1, and scheduling/reordering really only comes into play when non-sequential writes across multiple spindles?

I appreciate any feedback.