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I've created a RAID 5 device block by combining 4 HDDs.

The name of my device is md1.

But the /sys/block/md1/queue/scheduler file outputs "none" on doing cat.

And also after editing it using vim its throwing

/sys/devices/virtual/block/md1/queue/scheduler" E667: Fsync failed

I also tried using sysctl.conf and by adding

block.md1.queue.scheduler = deadline

But again it throws

error: "block.md1.queue.scheduler" is an unknown key

I'm really out of options. Please help me out.

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Here be dragons! –  Tom O'Connor Feb 7 '13 at 9:51
    
Which OS distribution/version/kernel are you using? That's a very pertinent detail! –  ewwhite Feb 7 '13 at 9:54
    
I'm using CentOS 6.3 –  Nilesh Feb 7 '13 at 9:56
2  
IIRC scheduling is set on the physical devices (sda/sdb/sdc...) not the md dev –  symcbean Feb 7 '13 at 10:07
    
@symcbean That thought came to my mind as well. But I was not sure about it that it can't be done. –  Nilesh Feb 7 '13 at 10:19
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1 Answer

up vote 4 down vote accepted

You can apply the I/O scheduler to the real block devices; e.g. your /dev/sdX devices or default a global append to the kernel boot command line in /etc/grub... (add elevator=deadline)

But since you're using EL6 (Red Hat, CentOS, etc.), the most effective approach would be to use the tuned framework.

In your situation,

yum install tuned tuned-utils

Then choose a profile which will provide the right setting for your application. For instance:

tuned-adm profile throughput-performance

or

tuned-adm profile enterprise-storage

Tuned chart

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Thanks. I did it but still the scheduler file for RAID block outputs "none". –  Nilesh Feb 7 '13 at 10:14
    
@Nilesh What did you do? –  ewwhite Feb 7 '13 at 10:14
    
I installed and set the profile to throughput-performance and then checked the file /sys/block/md1/queue/scheduler –  Nilesh Feb 7 '13 at 10:16
    
Look at the output of when you run tuned-adm profile throughput-performance. It will say something like: Applying deadline elevator: sda sdb sdc sdd [ OK ]. As I stated in the answer above, the elevator settings are applied to your block devices... your individual disks, NOT the mdX device! –  ewwhite Feb 7 '13 at 10:18
    
Yeah that happened. And I cross checked the sdX scheduler file and they had that change. –  Nilesh Feb 7 '13 at 10:20
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