FreeBSD 10.3 poor disk I/O as KVM guest

Posted on by Andy

I am using KVM on CentOS 6 (host) and FreeBSD 10.3 as a guest system. FreeBSD's hard disk write performance was horrible! It was about 2-5 MB/s! After searching some time, here the fix which led the write speed to 40 MB/s!

Open your VM config file with 

# virsh edit <SERVER>

then find your hard disk config line and change the cache and io paramter accordingly. Here the wonderful line which gave it a awesome performance boost: 

<disk type='file' device='disk'>
    ...
    <driver name='qemu' type='raw' cache='none' io='native'/>
    ...
</disk>

Save your config file and reboot your FreeBSD guest, you will see the difference is huge (at least in my case)