[ClusterLabs] GFS2 + KVM with qcow2 recommended IO mode

Andrew Price anprice at redhat.com
Wed Feb 28 10:14:40 EST 2018

On 28/02/18 14:03, FeldHost™ Admin wrote:
> Hello all,
> I have GFS2 cluster with KVM using qcow2 images. What is recommended IO mode? threads or native? I will be happy for recommendation and explanation.

You'd likely get a better answer from the QEMU folks, but:

As I understand it, with io=native qemu submits IO using OS-based aio 
(io_submit()) and with io=threads it handles its own async io using 
threading. To see what works best for you, it might be a good idea to do 
some perf testing of your intended workload with each i/o mode.

This talk covers the subject https://www.youtube.com/watch?v=Jx93riUF5_I

You didn't mention whether you're using qcow2 _for_ gfs2 but be aware 
that recent versions of libvirt will prevent non-raw images being made 
shareable due to the potential for corruption. See 
https://bugzilla.redhat.com/show_bug.cgi?id=1511480 for details.

Hope this helps,


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