[CentOS] IO Schedulers

[Barry Brimer]

> I'm on a quest to do some serious tuning to some of my production systems. All are on CentOS 5.x ranging from 5.0 to 5.4. I've been reading up on the various IO schedulers available in the kernel and I'm hoping some of you can lend some insightful suggestions. I typically have three classes of system in production:

> I welcome your suggestions and experiences. :-)

First and foremost, I think that the only correct answer to how to tune 
your system is "it depends".  There are lots of factors at play, although 
disk access is one of the largest, if not the largest factor that can be 
tuned.  There is no silver bullet answer here.  You need to make one 
change at a time, measure your system performance and compare.  Beginning 
with RHEL 5, you can select a different elevator algorithm for each block 
device .. which may be useful to you.  If possible, I highly recommend the 
RH442 - Red Hat Enterprise System Monitoring and Performance Tuning class 
offered by Red Hat.  It is very in depth and does a good job of covering 
material which by many respects is seen as "black magic".

HTH,
Barry