CFQ: 845 TpmC
DL: 2145 TpmCThis is a huge difference in performance between the two schedulers. How do you know if you are using the deadline scheduler? There are a few ways. The deadline scheduler can be enabled for all of your disks at boot time via the LILO or GRUB boot loaders. The scheduler can be changed by appending the string elevator=deadline to the boot line (file /boot/grub/grub.conf). If you issue the command cat /proc/cmdline this will display the kernel parameters that the system was booted with.
The second way of switching schedulers is to change it "on the fly." You can list all of the available schedulers, as well as determine which scheduler is current by using this command: cat /sys/block/drive/queue/scheduler where drive is the actual drive represented to your system (i.e. sda, hda). The list of schedulers is displayed, and the current scheduler is noted within square brackets. To change the scheduler, echo the name of the new scheduler to the meta-file from the previous command (as user root). Be careful when switching schedulers on the fly, as there is a possibility to hand the system.
In part 2, I'll go over my testing methodology and show how using the deadline scheduler with different types of RAID drive configurations and filesystem types affects the overall throughput of the system.
4 comments:
Some people also suggest noop scheduler. How does it compare to deadline? Have you benchmarked that?
have you tested the noop scheduler? In my tests it usually won on throughput. Of course that's with a decent raid controller which most db servers will have. Don't take too much notice of io benchmarks on e.g. A spare laptop :-0
I have been performing my testing on a Dell 2950 with a Perc/5 RAID controller. I did perform a benchmark with the noop scheduler and there was very little difference in performance to the deadline scheduler.
That seems consistent with what I observed then. I'm glad you did your tests on a raid controller. Some others have previously run performance comparisons on non-server hardware (sometimes laptops)
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