[CentOS] [OT] RHEVM List

Fri Jan 7 17:21:06 UTC 2011
Benjamin Franz <jfranz at freerun.com>

On 01/07/2011 05:02 AM, Nico Kadel-Garcia wrote:
> I was testing it with KVM, for comparison to VMWare, and didn't get as
> far as that. The network configuration, multiple disk at install time,
> and dog-slow performance of KVM prevented further exploration. KVM was
> being heavily advertised by RedHat so I wanted a look, and was
> completely underwhelmed. The requisite "bridged" network ports have to
> be set manually on the server, since the built-in network
> configuration tools have no clue how to do it. This means network
> pair-bonding has to be done in the guest domain, and it turned out
> that PXE didn't work at all in the guests.
> It was completely useless: hopefully RHEL 6 and CentOS 6 get it right.

I'm successfully running KVM on top of Ubuntu 10.04LTS with CentOS5.5 
guests with virtio ethernet drivers. I've got my physical ethernet ports 
bonded (three pairs of two) and bridged to the guests such that they 
don't even know any magic is happening. The configuration is completely 
non-obvious (and way under documented) but not very complex to 
implement. The only performance issues I have encountered so far are 
linked to the abysmal disk write performance of the qcow2 image file 
format. It can be partially ameliorated by turning on writeback for the 
disk images (or by using raw format instead of qcow2). I've got 17 
running guests on one machine (8 cores, 32GB RAM, 2+ TB of battery 
backed RAIDed disk) and it is working like a champ. The only major 
complaint I have is that by default 10.04LTS doesn't cleanly shutdown 
the VMs on a reboot or shutdown - instead just effectively 'pulling the 
plug' on them. RH apparently does the same thing in 5.x: kills guests 
rather than shutting them down on reboot/shutdown. :O

I had to do some surgery on the init system to make it do a clean 
shutdown on guests (and hid  'shutdown' and 'reboot' behind some scripts 
that do a parallel vm shutdown before actually calling the real 
'shutdown' or 'reboot' just to be really sure).

Benjamin Franz

Benjamin Franz