fs_async & create_fastlinks???

[Joeriz Agtay]

I'm running very slow and looking on kernel parameters. Can you give me more info when to change this parameters? My current setup is fs_async=0 & create_fastlinks=0. My data disk is using EMC and all datafiles for Oracle database are using raw devices. I'm sitting on N-class 8-way proc with 6 GB of memory. Thanks.

[Steven Sim Kok Leong]

Hi,

First, you need to identify where the performance bottleneck is, before you should decide on which kernel parameters to change.

To identify the bottleneck, make use of Glance, top, sar or any other performance statistical tools.

Hope this helps. Regards.

Steven Sim Kok Leong
Brainbench MVP for Unix Admin
http://www.brainbench.com

[Steven Sim Kok Leong]

Hi,

If you are facing an I/O bottleneck, in additional to sar and glance, you can make use of iostat to monitor your I/O performance.

From glance, you can check the real-time I/O statistics for each disk device, identify which LVs are having the most I/Os on this disk device. Subsequently, load distribute the more I/O-intensive LVs from this disk device to less I/O-intensive other disk devices via pvmove if it is in the same VG.

In my environment, for database files which are randomly accessed, you should configure LV striping for maximal I/O performance except for the LVs housing redo logs and archive logs. We are using hardware-based RAID 1 in our XP256 for our databases. We make an effort to split the I/O across as many ACP and as many disk spindles were possible.

Hope this helps. Regards.

Steven Sim Kok Leong
Brainbench MVP for Unix Admin
http://www.brainbench.com

[Steven Sim Kok Leong · Accepted solution]

Hi,

I forgot to talk about the kernel parameters fs_async and create_fastlinks that you highlighted.

create_fastlinks is used to create HFS symbolic links in a manner that reduces the number of disk-block accesses by one for each symbolic link in a pathname lookup. Since you are using raw devices, you do not need to activate this parameter thus it should remain as 0.

fs_async is used for selecting whether you want synchronous or asynchronous writes of filesystem data structures to disk. Again, you are using raw devices not filesystems, thus this parameter does not apply. It can be either 0 or 1.

Hope this helps. Regards.

Steven Sim Kok Leong
Brainbench MVP for Unix Admin
http://www.brainbench.com