How to get I/O priority to work on Ubuntu?

Ubuntu has ionice, but as far as I can tell, it does absolutely nothing.

I suspect this is because Ubuntu replaced cfq with deadline and deadline doesn't support priorities.

Is there any possible way to have prioritized I/O on Ubuntu anymore?

EDIT: The context is that I have a database restore that easily consumes all my I/O and renders my system unusable until it has finished. I'd like it to remain usable for other tasks.

Solution 1:

You have to change your scheduler from deadlineto cfq.

You can do that per blockdevice and non permanent via

sudo echo cfq > /sys/block/<blockdevice>/queue

Or for the whole system, permanent via grub, with adding the elevator=cfqparameter to the grub commandline options.

This is an excellent post explaining how you can do that.

What the drawbacks of such a change are is better covered elsewhere.

The TL;DR is

According to the test results, each scheduler has different advantages over others. CFQ scheduler is suitable for the systems that require balanced I/O access and do not need process prioritization. Deadline scheduler has better performance on read-intensive works. Noop is for the systems on the cloud or hypervisors. BFQ performs better on interactive use-case scenarios. Noop is the simplest scheduler and it is considered to have the potential for optimized new implementations targeting SSD block devices.