[CentOS-virt] tick divider bugs

Mon May 5 09:06:23 UTC 2008
Allen Tsang <atsang at advance.net>

Hey folks,

By Paravirtualization, I mean the installation of "tools" or "guest 
additions" type packages, which present virtual interfaces to the guest 
OS.  So in VMware, a component of this would mean setting 
"ethernet0.virtualDev = vmxnet", and having the tools modules 
pre-installed.  A fully virtualized OS for VMware would support all that 

 From Wikipedia:
In computing, paravirtualization is a virtualization technique that 
presents a software interface to virtual machines that is similar but 
not identical to that of the underlying hardware.

Paravirtualization may allow the virtual machine monitor (VMM) to be 
simpler or virtual machines that run on it to achieve performance closer 
to non-virtualized hardware. However, operating systems must be 
explicitly ported to run on top of a paravirtualized VMM. Owners of 
proprietary operating systems may decline to allow paravirtualization 
for strategic purposes.

I'm neurotic about paravirtualization because, well, we roll our 
organization's production systems on VMs, so I want minimal performance 
hit if possible across the board.  I'm sure some of you are thinking 
right now how foolish I am for doing this.  In reality, cost savings in 
labor through all of the flexibilities of a fully virtualized 
environment is more important to us than raw performance and low latency.

One problem with setting your VM template to utilize virtualDevices in a 
production environment currently is the inability to PXE boot the 
machine to provision your host, because no commerical distro or 
operating system I know of, Linux, BSD, Solaris or otherwise, currently 
offers an out-of-the-box module support for virtualization in their 
install initrd, for various licensing and technical reasons (the 
open-vm-tools effort would likely solve this in the near future).  OHAI 
Trolls who can't read: YES YOU *CAN* PXEBOOT w/VMXNET (NOT 

I know of tru's efforts and others on this front and I really appreciate 
the knowledge they have brought to the table, but I feel that it's about 
time that some dedicated entity step in and 'solve' this problem (we've 
written kickstart+firstboot-type scripts that eliminate the 'work' of 
managing hundreds of VMs and their installation of tools, but through 
the whole process we have wished for Our Favorite Community Enterprise 
OS to support this stuff OOB so we didn't need to do the work.  Lazy 
Sysadmins are lazy).  One man cannot keep such a beast up to date; it 
needs to be a dedicated effort or project.  The complexity of 'doing VMs 
right' is getting to the point where it requires a virtualization expert 
to be staffed (consider the ever-present Time Sync Issue, which requires 
customization on the Host configuration AND the Guest OS).  This is 
unacceptable; we either need virtualization software that is a little 
more clever or we have to step in on the application layer and have the 
OS live closer to the host hardware.  Also, there's a great deal of 
untapped potential in having at least a greater set of conservative 
message passing between the Guest OS and Host / VM Infrastructure, 
shared storage amongst different hosts over the attached SAN, etc etc... 
skies the limit.

This might be a direction that Big Mommy RedHat should/would eventually 
take.  I'm not a big fan of CentOS mini-forks of kernels myself (e.g. 
centosplus, -vm, etc), since it kinda defeats the 'point' if you know 
what I mean.

/me crosses fingers that Sun + InnoTek makes a really kickass VirtualBox 
for the Enterprise that develops a much better solution, or better yet, 
a *truly* embedded virtualization solution (Hey, anyone from Sun 
Engineering on this mailing list?  Imagine memory and storage pooling on 
the hardware layer over something like infiniband, guys).

Then again, cloud computing, future is bright, sunglasses + igloos, 
teotwawki, lol.

- allen tsang

Daniel de Kok wrote:
> On Mon, May 5, 2008 at 5:13 AM, Allen Tsang<atsang at advance.net>  wrote:
>>   Speaking of which, I was talking to some friends about building a fully
>> paravirtualized rhel/centos that works with xen, vmware, virtualbox, etc.
>> Do you guys feel like that's a product you would consider using?
> I suppose you mean "fully virtualized", since VMWare and VirtualBox do
> not paravirtualize? If so, True provides VMWare images of CentOS 4 and
> 5. They should be easy to modify for VirtualBox and qemu as well:
> http://dev.centos.org/~tru/vmware/
> Take care,
> Daniel
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