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n00b
Joined: 10 Sep 2003
Posts: 16
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 Posted: Sun May 14, 2006 3:19 pm Post subject: Right I/O scheduler for hardware RAID |
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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This is a little bit outdated but it's still interesting.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
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Henri |
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tnt
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Joined: 27 Feb 2004
Posts: 1121
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| Posted: Sun Jun 11, 2006 11:46 pm Post subject: |
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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...
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