[CentOS] Disk Elevator

Matt wrote:
> Can anyone explain how the disk elevator works and if there is anyway
> to tweak it?  I have an email server which likely has a large number
> of read and write requests and was wandering if there was anyway to
> improve performance.
> 

I assume you are talking about Centos 3.x with the 2.4 kernel.I know it 
is heavily patched but I don't think it has the complicated i/o 
schedulers you find in 2.6

You use elvtune to tweak it. Basically you just define the max length 
the write queue can be before attention will be given to reads and 
likewise for the read queue. man elvtune for more information.

I do not have a 2.4 kernel box anymore but I think you can try 'elvtune 
-r 128 -w 128 /dev/device' and see if that helps. 'elvtune /dev/device' 
will show you the settings being used. If you are using ext3, you 
probably also want to look at tweaking /proc/sys/vm/bdflush. Look here 
for more information:

http://people.redhat.com/alikins/system_tuning.html