[ale] Virtualization

[Christopher Fowler]

JK wrote:
> So I'm running VirtualBox on a 3Ghz dual-proc P4 with 3GB of
> RAM.  (Maybe it's just hyperthreading, but /proc/cpuinfo
> reports two CPUs, and I haven't looked inside the box. Got
> the machine from my employer after a cancelled project.) The
> host OS is Ubuntu Intrepid, and the guests are mostly WinXP.
>
> Whenever a guest machine does the tiniest little thing --
> scroll a command window a couple of lines, for example --
> it seems to peg the guest's (virtual) CPU, and really
> elevate the CPU usage on the host.  This seems unnecessary,
> and I'm wondering if VMWare or Xen or some other virtualization
> technology makes better use of the underlying hardware.
>
> Any experiences to share?
>
>   
This is my experience as well.  I think many companies look at 
virtualization as a way to save
money on hardware.  Yes it does but the guest must be suited for it. 

I run about 5 guests on a CentOS 5.2 host with Server 2.0.  We have one 
Windows 2003 Server guest
and the rest are CentOS 5.2.

Sometimes when I edit a file on a guest with vim it may take a second 
for vim to load it or for it to write
it.  It is almost as if the guest is blocking in I/O to the disk.  When 
typing over SSH I can sometimes
feel a latency on the guest I do not feel on real servers. 

For the most part the average load on each guest is probably less than 
0.25.  This works well.  rarely
we get a runaway process on one of the guests.  When this happens, each 
guest takes a major performance
hit.  They all share the same 2 CPUs on the host.  I wish there was a 
way in server to limit a guest to
a certain percentage of the host's CPU.