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Disk scheduler of VM instance.

asked 2016-10-04 01:02:01 -0500

syko gravatar image

The host machine and the instance both use Cent OS 7 (3.10.0-327.10.1.el7.x86_64). VM uses KVM.

I checked the io scheduler of VM instance as follows:

cat /sys/block/vdb/queue/scheduler

It gives "none" (which is not the case for the host machine)

Does it mean that VM instance has no control over the disk io scheduling?

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answered 2016-10-04 13:46:14 -0500

This is correct - this isn't implicity saying the VM has no control, it's simply saying that it doesn't make sense to run an elevator on virtual devices.

Instead, the I/O is passed straight down the stack to the real disk where there is a single elevator managing all I/O to that disk, whether it comes from different virtual machines, or logical volumes. In your case, this means that the scheduler on the host machine is the one that's being used for that device.

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Asked: 2016-10-04 01:02:01 -0500

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Last updated: Oct 04 '16