Using Ubuntu 64 bit server

Larry Alkoff labradley at
Wed Oct 20 18:43:59 UTC 2010

J wrote:
> On Mon, Oct 18, 2010 at 18:31, Larry Alkoff <labradley at> wrote:
>> I plan to purchase a 64 bit motherboard and memory
>> to run as a server under Ubuntu 64 bit AMD (includes Intel) server
>> 10.04.1.  The memory is 16 gigabytes.
>> The same motherboard will run various OS under KVM virtualization including:
>> Ubuntu Desktop 32 or 64 bit version
>> Windows XP
>> Windows 7
>> Apple OS X (possibly)
>> My questions are:
>> 1.  Will either 32 bit or 64 bit Ubuntu work well?
>>        Which is recommended?
> Do you mean for the host OS or for a VM?  I know you said above that
> you wanted to use Ubuntu 64bit as the host OS, but this question is
> ambiguous enough that you could clarify... However:
> If you mean host OS: then 64bit is the way to go in your case, IMO.

I am running Ubuntu server 10.04.1 LTS.  I prefer LTS and hope that the 
server version will not have changed much in 10.10.

> If you mean as a VM OS, either one should work fine...  Caveat: I've
> not fared well with kvm or qemu on Linux... I've run Xen for years in
> Red Hat to varying degrees of success and with my current job I use
> VirtualBox.  I tried KVM a while back but could never get the VMs to
> run with any sort of stability, when they'd run at all.  SO YMMV, it
> could very well have been something bone-headed that I did.  FWIW, I
> know KVM does work as I also have access to a server at work that
> functions as a KVM host...

My other OS's will be
Kubuntu 10.04x LTS 32 bit (my primary desktop ;-)
Windows XP
Windows 7 (as yet untried)
Mac OS X (possibly but I have other Macs)
Test versions of Ubuntu/Kubuntu

>> 2.  Will other 32 bit OS like XP work?
> Yes.  I've run various 32bit VMs on my 64bit Ubuntu systems with no
> problem. I've done the same on the KVM host at work.
>> 3.  How does the 64 bit server handle 32 bit code?
>>        If by thunking, is there any speed degradation?
> No idea, unfortunately...  I want to say that there is some thunking
> that occurs, but honestly, that's too far into dark kernel magic
> territory for me to give you a reliable answer.
> I can say that a VM will never run as fast as a bare metal system,
> there will always be a degredation in speed.  Especially when you
> start looking at HVM vs Paravirtualized.  There's a reason why
> virtualization providers started providing paravirt driver packs for
> HVM guests... Perhaps someone more in the know about KVM could explain
> whether KVM uses hardware virtualization fully (like Xen does) or if
> it's all paravirt.
> However, I'm willing to bet that you're going to see more of a
> bottleneck in disk I/O than you will anywhere else.  Depending on how
> many VMs you're running, and where their filesystems are stored, disk
> I/O is far more likely to cause performance issues, in my own
> experience.  On my uber-laptop I can run only one at a time (two if
> I'm really careful about what each is doing) because they're stored on
> a single SATA disk.  On servers in the past through Xen, Ive seen
> varying degrees of bottlenecking at the disk level depending on
> whether the VMs were stored on a local RAID device, a SAN share, iSCSI
> or external SCSI RAID.
> Of course, how much ram each uses can also cause performance issues
> when you're running more than one VM at a time...
> But in any case, while I can't directly answer your question, I can at
> least pass that bit of knowledge along.
> Cheers,
> Jeff

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