Gentoo Forums
Gentoo Forums
Gentoo Forums
Quick Search: in
Right I/O scheduler for hardware RAID
View unanswered posts
View posts from last 24 hours

 
Reply to topic    Gentoo Forums Forum Index Documentation, Tips & Tricks
View previous topic :: View next topic  
Author Message
Pointer
n00b
n00b


Joined: 10 Sep 2003
Posts: 16

PostPosted: Sun May 14, 2006 3:19 pm    Post subject: Right I/O scheduler for hardware RAID Reply with quote

Linux 2.6 - I/O schedulers

http://www.unidata.ucar.edu/support/help/MailArchives/ldm-users-list/msg03994.html
Quote:
I was having some serious I/O slow downs with 2.6.11 and my 3ware raid card. One of the problems was the I/O scheduler. The kernel builds with the "anticipatory" I/O scheduler as the default. However, if you read the documentation in the kernel on this scheduler in "Documentation/block/as-iosched.txt" you find the following:

"Also, users with hardware RAID controllers, doing striping, may find
highly variable performance results with using the as-iosched. The
as-iosched anticipatory implementation is based on the notion that a disk
device has only one physical seeking head. A striped RAID controller
actually has a head for each physical device in the logical RAID device."


Choosing an I/O Scheduler for Red Hat® Enterprise Linux® 4 and the 2.6 Kernel
http://www.redhat.com/magazine/008jun05/features/schedulers/
Quote:
The Completely Fair Queuing (CFQ) scheduler is the default algorthim in Red Hat Enterprise Linux 4. As the name implies, CFQ maintains a scalable per-process I/O queue and attempts to distribute the available I/O bandwidth equally among all I/O requests. CFQ is well suited for mid-to-large multi-processor systems and for systems which require balanced I/O performance over multiple LUNs and I/O controllers.


I/O Benchmarking Guide
http://www.3ware.com/kb/attachments/Linux2.6WP_0701.pdf

3Ware specific topic
Performance/Optimization: How can 3ware read performance be increased in Linux


Selecting Scheduler
For example, if your raid device is "/dev/sda", you can see the current scheduler setting by typing:
Code:
cat /sys/block/sda/queue/scheduler

You can change it to "cfq" type typing:
Code:
echo "cfq" > /sys/block/sda/queue/scheduler


/etc/lilo.conf

Code:
image=/boot/vmlinuz-2.6.12
  label=linux
  read-only
  append="elevator=cfq"   
  root=/dev/hda6
  initrd=/boot/initrd-2.6.12.img

Pinpoint the append line!

ps.
This is a little bit outdated but it's still interesting.
Performance Tips for Kernel 2.6

--
Henri
Back to top
View user's profile Send private message
tnt
Veteran
Veteran


Joined: 27 Feb 2004
Posts: 1130

PostPosted: Sun Jun 11, 2006 11:46 pm    Post subject: Reply with quote

here:
http://forums.gentoo.org/viewtopic-t-451428-highlight-scheduler.html

I've found this:
Quote:
ANTICIPATORY (AS): This is a decent scheduler, it works well with all file systems, Only use it on older drives, particulary drives that spin at 5400rpm or less (many laptop hard drives)
DEADLINE: This is a surprising scheduler, it is light and awesome. It performs the best on most file systems, including reiser4. Only use it on drives that spin faster than 5400rpm
CFQ: Only use it on ext3, this scheduler doesn't work as good as AS or Deadline on anything else.


Than again, I guess this is desktop system related...
_________________
gentoo user
Back to top
View user's profile Send private message
Display posts from previous:   
Reply to topic    Gentoo Forums Forum Index Documentation, Tips & Tricks All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum