Choosing the right KVM version for production on CentOS 5.3

Choosing the right KVM version for production on CentOS 5.3

[Federico Simoncelli]

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?

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?

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?

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.

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?

I also heard that RHEL 5.4 will be featuring kvm, if the kvm redhat
team is already working on these same issues I'd be definitely pleased
to contribute with my current testing experiences. Feel free to
contact me.

Thank you in advance,
-- 
Federico.

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

[Avi Kivity]

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.