[CentOS] CentOS 5.2 VMI support

nate centos at linuxpowered.net
Fri Jul 11 00:31:22 UTC 2008

Ruslan Sivak wrote:

> Does it just require a kernel recompile?  Is there maybe one available
> somewhere?

No it requires changes to the kernel itself, changes which I don't think Red
Hat will introduce in a minor release as their current VM stuff is Xen based
which has it's own paravirtualization support in the existing kernel(pre
VMI). I read that Red Hat is moving towards KVM though, I don't have any
knowledge on that project, maybe it uses VMI as well.

> Would
> it give me improved disk access speed?

I doubt it. I'm planning on using it mainly so I can run a couple of NTP
servers in VMs. Even though it's still not officially supported my experience
shows that NTP *will never sync* in VMWare with normal virtualization. But
with VMI/paravirtualization I've had a ntp daemon synced for weeks so far. I
don't plan to use VMI for anything other then a couple bare bones VMs to run
NTP. Then the rest of the VMs will run ntpdate every minute against them,
and the non VMs will run ntp daemons and sync with them. The internal vmware
time sync(at least in ESX) doesn't work too well in my experience so I just
turn it off and use ntpdate instead.

Disk access speed is limited to the speed of the I/O subsystem. VMware has
recently demonstrated a ESX system being able to sustain 100,000 I/Os per
second (maxing out ~500 15k RPM disks), and that wasn't using
paravirtualization. If you can get 100k IOPS with normal virtualization...


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