[CentOS-virt] Best practices on KVM systems

Fri Jan 11 14:21:31 UTC 2013
Nico Kadel-Garcia <nkadel at gmail.com>

On Fri, Jan 11, 2013 at 8:51 AM, Luca Gervasi <luca.gervasi at gmail.com> wrote:
> Hello,
> i'm trying to create some best practices on my centos 6.3 / libvirt /kvm
> hypervisors.
> Actually, i use NFS as shared storage backend for every VM and make
> reasonable use of the KSM (enabling it into qemu.conf).

If possible, use "autofs" for the NFS shares. This is because failures
to connect at boot time will leave NFS unavailable for the guests,
even with a simple KVM restart.

> Every VM is configured with VirtIO drivers (when possible) and the disks use
> none as cacheing method to allow me live migration.

Review your back end storage. If it's a NetApp, especially, make sure
all VM partitions are aligned for 4096 byte block boundaries. (See the
NetApp white paper on this issue.) Otherwise, the NetApp is doing a
lot of unnecessary re-alignment work to talk to its own back-end
disks, and this can actually cause critical NetApp slowdowns.

> I'll be happy to know if there are some more improvements i can implement.

Look into pair-bonding for the KVM hypervisor itself. I published
notes on this at my last workplace, at
Also look carefully into the use of jumbo frames for NFS.

Unfortunately, that job just ended, so I'm actually looking for work
in the Boston area. (If you see anything for me, let me know!)

> Please share your knowledge.
> Thanks in advance
> Luca Gervasi