On Jan 5, 2006, at 9:57 AM, Kielek, Samuel wrote:
Actually, it's running on top of a stripped-down Red Hat.
That is incorrect. ESX does not run on Red Hat or any other Linux
based
OS. I think you are referring to the service console which is based
off
of an older version of Red Hat (7.x).
It sure looks to me like there's a minimal Linux running, and that
that Linux loads a small set of filesystem and network drivers, and
then loads the vmkernel kernel module, which in turn provides
scheduling support for the service console and virtual machines
(remember that VMWare ESX long predates the replaceable-scheduler-as-
a-kernel-module support that came along in 2.6).
http://www.vmguru.com/modules.php?name=News&file=article&sid=36
seems to bear this out.
However, from that page, it's also clear that vmkernel itself loads
its own device drivers, which suggests that Linux is used as a
bootstrap and that vmkernel then replaces it....but then there's also
a way that the vmkernel can in turn use Linux device drivers.
I guess, then, the question is "to what degree does vmkernel ride on
top of the Linux kernel, and to what degree does it replace it?"
I don't know the answer to that one. Clearly, it's conceptually
similar to SSLSERV: once you've loaded the magic module what you have
left is a special-purpose appliance and not a general-purpose Linux
system. SSLSERV is still very much Linux while running, though
(albeit without network services!), and it's a lot less clear that
ESX is.
However, the service console is
not required for operation. In fact, you can shut the service console
down altogether and your guests will continue to run just fine.
Sure, but you can't shut down the Linux kernel which has loaded the
vmkernel module.
I think
people mistakenly think that the ESX hypervisor runs under Linux
because
it uses a familiar Linux bootstrap process, but that is where the
similarity ends..
I'd disagree, since the vmkernel functionality is provided as a Linux
kernel module. I suppose it depends on where you think bootstrap
ends and normal system operation begins.
Adam
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