aacraid driver 1.1-5[2449]-suse performance issue with Dell PERC 3/DI controller

This document (7001104) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 10 Service Pack 2

Situation

aacraid driver 1.1-5[2449]-suse  is causing  slow performance with Dell PERC 3/DI controller on SUSE Linux Enterprise Server 10 Support Pack 2.

Running sar linux command showed the servers running with very high i/o wait times under SUSE Linux Enterprise Server Support Pack 2.

The same model server running SUSE Linux Enterprise Server Support Pack 1 did NOT have the high i/o wait.

Other Dell PowerEdge Servers like 1650, 2550 and 2650 have the Adaptec PERC 3/Di Raid Controller and they should have the same problem.

There is some information on the Dell mailing lists that indicate that the aacraid driver version 1.1-5 is not working correctly with 2.6.16 kernels:
- http://lists.us.dell.com/pipermail/linux-poweredge/2006-April/025337.html
- http://lists.us.dell.com/pipermail/linux-poweredge/2006-April/025334.html

 

Resolution

This has been resolved in the kernel 2.6.16.60-0.34, which was released on the 29th of January 2009.
From the changelog :
* Thu Nov 06 2008 - hare@suse.de
- patches.drivers/aacraid-no-wce: aacraid performance issue with
  Dell PERC 3/DI controller (bnc#400783).

The reason for the problem is that having write caching enabled (WCE) both in the linux kernel and on the RAID controller is inefficient. So the patch basically disables WCE in the OS when dealing with aacraid.

On SLES 11 this patch does not exist, but the way to disable WCE for aacraid is to set the parameter
caching=2
for the aacraid module.
Running with the default configuration has been observed to lead to a 15 to 20 % write performance degradation on e.g. tests with the bonnie file system benchmark utility included in SLES.

Use the following procedure to implement this parameter :
  1. Add the following line to /etc/modprobe.conf.local :
    options aacraid cache=2
  2. If aacraid is loaded in initrd (is listed in INITRD_MODULES in /etc/sysconfig/kernel), then the initrd needs to be recreated with the command
    # mkinitrd
  3. Reboot the system

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

  • Document ID:7001104
  • Creation Date: 05-Aug-2008
  • Modified Date:12-Mar-2021
    • SUSE Linux Enterprise Server

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