Re: Choosing the right KVM version for production on CentOS 5.3

[Avi Kivity <avi@redhat.com>]

Federico Simoncelli wrote:
> Hi all,
> I'm trying to switch from xen to kvm. I already successfully installed
> and tested kvm-84 on a CentOS 5.3 but before put it in production I'd
> like some advices from you:
>
> 1) I'm trying to settle and use one version of kvm maybe backporting
> some patches when needed. What version do you suggest me to use in a
> production environment?
>   

For production, use kvm-kmod-2.6.30-rc8 (and its updates), and 
qemu-kvm-0.10.5 (and its updates).

> 2) I'm pretty much confused about kvm-x and qemu-kvm, anyway I used
> kvm-84 with no problem and lately I'm testing qemu-kvm 0.10.5 with the
> kvm-84 kernel module. Is this combination (kvm-84 kernel module and
> qemu-kvm 0.10.5) right? Is there a better one?
>   

kvm-xx are really development snapshots; they undergo testing but they 
don't get fixes backported.  If you are interested in minimal churn and 
maximum stability, use the combination above.

> 3) What is the difference between qemu-kvm 0.10.5 (on the kvm
> sourceforge site) and qemu 0.10.5. Which one do you suggest me to use
> in a production environment?
>   

qemu-kvm-0.10.5 is qemu-0.10.5 with improved kvm integration (for 
example, smp) and a few additional features.  Use qemu-kvm 0.10.5 for 
best performance and stability.

> 4) I saw that the rpm packages for CentOS (provided by lfarkas.org)
> are based on qemu 0.10.4, is there a reason? is it a very stable
> release? I tried to contact Farkas but I had no reply yet.
>   

No idea, I hope the packages will be updated soon.

> The last question might be split in a new thread:
>
> 5) I tried to use qcow2 images with migration (storing them on gfs)
> but the migration fails very frequently (mostly on heavy disk load). I
> think the problem is that the new qemu-kvm (the -incoming one) reads
> (or tries to read) the qcow2 headers before receiving the full ram
> memory image and during the transfer time the qcow2 file get modified
> by the old qemu-kvm (the dying one) which flushes the disk cache. Is
> anyone else trying to let qcow2 work with migration?
>   

qcow2 works with migration, there might be issues with GFS though.  Can 
you try qemu-kvm 0.10.5 with qcow2 over NFS?  If that works for you, we 
can try to debug the GFS issue.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.