Using Ubuntu 64 bit server

Larry Alkoff labradley at
Wed Oct 20 19:03:16 UTC 2010

Christopher Chan wrote:
> On Tuesday, October 19, 2010 08:16 AM, 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.
> I have a server that has 16G of RAM too where I will be running multiple 
> Windows servers. Oh, the motherboard does not determine whether things 
> are 64-bit or not. The server I use has two AMD Opterons supplying 
> 24-cores in total, two SAS2 host controllers and will eventually have 36 
> disks connected (right now there are only 12, two as system disks, 10 in 
> a raidz2 array with one as a spare) and a dual-port Intel gbit nic 
> onboard and an addon 4 port intel gbit nic.
>>> The same motherboard will run various OS under KVM virtualization including:
>>> Ubuntu Desktop 32 or 64 bit version
> Why Larry? Just curious.
I ask about Kubuntu desktop 32 or 64 bit version for 2 reasons:
   1.  I know that there used to be a speed degradation problem caused 
by "thunking" needed to convert 64 bit system calls into 32 bit for 
those OS that needed it.  I'm still trying to find out if Ubuntu 
"thunks" and whether it is still a problem.
   2.  I run other Kubuntu 32 bit desktops.  They are my 'production' 
systems that are in daily use.  They all use rsync to both to keep the 
data the same and backed up.  My concern is that there will be 
differences in the data caused by the different 32/64 bit systems and 
I'd prefer not to have those kind of complications.  Also not all of my 
computers will support 64 bits so I'd rather stick with the 32 bit 
systems for a while.

>>> Windows XP
>>> Windows 7
> there a paravirtualized graphic driver for Windows under KVM 
> available yet? No? Ah shucks.

>>> Apple OS X (possibly)

> /me stares. Let us know if you get that working Larry. :-D
I'll let you know.
But first I have to get Kubuntu working virtualized.  Know any good 
sources of info?

>>> 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.
>> 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...
> KVM is stable when I tried it on Hardy...just don't expect any 
> speed/smooth video playback. Xen on the other a very intrusive 
> solution compared to KVM. Never found it stable even with Linux guests.

My instinct is to try KVM first since it's a part of Ubuntu and the kernel.

>>> 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.
> Jeff, you've got things backwards.
> KVM must have hardware virtualization available as it is hardware 
> virtualization module but it does support paravirtualize stuff like disk 
> and nic i/o via virtio. Xen, depending on version, is most certainly NOT 
> hardware virtualization. Xen is initially paravirtualization only and 
> therefore only Linux guests and other xen-enabled operating systems were 
> supported. It has, of course, added hardware virtualization support in 
> version 3.0 and so you can run unmodified Windows on Xen with version 
> 3.0 onwards.

I'm not sure of the difference between hardware virtualization vs 
paravirtualization unless para refers to software.
I'm new to this but since I have just gotten the server working it's 
time to learn all about virtualization.

>> 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.
> If Larry has enough throughput, virtio should help plenty. I have got 
> very decent disk performance under KVM with virtio for Windows. No 
> virtio then yes, forget it. It will crawl.

I read about vertio (actually virtfs) in Linux Pro Journal (Sept 2010) 
but there was a comment in the article that a maintainer has not yet 
been found for (K)ubuntu which I take means KVM.

Again, I'm new to virtualization (but not Linux) so I'm looking for all 
the info available.
>> 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.
> You could at least verify all your bits of knowledge before passing them on.

Larry Alkoff

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