[Openstack] Disk performances much slower in Centos 6.7 guests than on ubuntu 14.04 guests

Rick Jones rick.jones2 at hp.com
Thu Aug 20 18:06:08 UTC 2015

On 08/20/2015 10:39 AM, J-P Methot wrote:
> Hi,
> I've made a custom centos 6.7 image on a proxmox with kvm hypervisor
> with the goal of using it with openstack. I setup all the necessary
> cloud-init packages that are needed by openstack. Everything seems to
> work fine on openstack, except that the drive speed in fio is about 50%
> of what I can achieve on other images.
> Basically, on a ubuntu 14.04 with the following FIO command, I can reach
> about 1 GB/sec :
> fio --name=testfio --filename=testfio --bs=4m --rw=write --size=5g
> However, on my centos 6.7 image, I will only reach about 400 MB/sec. Why
> is there such a huge discrepancy between both OS? I've always used
> virtio, both on the proxmox hypervisor and on openstack.

I cannot speak to disc performance, but I can say there is a large 
difference in network performance between an instance running CentOS7 
with its 3.10 kernel, and an instance running either 14.04 (3.13) or 
15.04 (3.19).  There were virtio_net driver changes around buffer 
handling which appear to be the cause.  Perhaps something similar 
happened for the disc I/O path and what is likely the even older kernel 
in CentOS6?

happy benchmarking,

rick jones

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