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Does ionice work in Software-RAID environments? I cannot set the CFQ scheduler for the md devices, because there is no file /sys/block/md0/queue/scheduler . It seems that the scheduler settings for the underlying disks are not propagated to the raid devices.

Ideas?

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2 Answers 2

Disk i/o scheduler are set per spindle. You can change the scheduling algo for /dev/sda,sdb etc which are real, hardware , devices in your system. Software raid block devices are virtual.
Ionice is not related to software raid and it simple gives priority of one process over another when accessing the storage. So yes, you can use it with no matter what type of storage you use.

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Please have a look at my config and tests: gist.github.com/222323 Priority settings are at least ignored for my dd benchmarks. Do you have an explanation? Thanks! der Flo –  der_flo Oct 30 '09 at 13:01
    
I/O prioritization helps (and can be observed) when you have concurrent disk operations and processes fighting for block access. Redo your tests with multiple dd running at the same time but different priorities. –  Lorinescu Oct 30 '09 at 16:54
    
@Lorinescu: Of course I ran two "dd" pairs at the same time. Af first the ones with dsync, later the pair without dsync. Sorry for the vague gist. –  der_flo Nov 2 '09 at 8:22
    
what kernel version ? if i remember correctly io prioritization works from 2.6.13 and up –  Lorinescu Nov 19 '09 at 23:42
    
Ubuntu Karmic == 2.6.31 –  der_flo Nov 26 '09 at 10:53

Chris Siebenmann recently came to the same conclusion as you: ionice has no effect on either "software raid" (I presume this means MD) or LVM.

http://utcc.utoronto.ca/~cks/space/blog/

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