[SAC] Virtual Machines for Services

[shawn barnes]

I looked into and tested Xen about a year ago when i was deciding on a
virtual machine solution and I didn't find any real difference in
performance between Xen and vmware.  In the end i went with vmware
(would of preferred Xen b/c of it's OSS nature) but, it wasn't as
flexible nor as portable as vmware.

For vmware the general rule of thumb i've used for figuring out memory
resources is.

Amount of memory configured for each vm  
+ (50MB * # of vms)
+ 24MB (virtualization layer) 
+ 200MB (service console) 
+ (6% min free memory level) 
= min amount of ram needed. 

I'm not sure what the comparable thumb rule for Xen is.

shawn

On Tue, 2007-11-20 at 20:06 +0100, Mateusz Loskot wrote:
> Frank Warmerdam wrote:
> >
> > I understand that Xen requires kernel modifications, and doesn't work well
> > with some older systems.  Who is familiar with those limitations?  For
> > instance, I'd like to be able to run VMs on "osgeo2" but I think it is
> > running a somewhat antique RHEL, is that right?  Will it support Xen?
> > Can we even run the vmware player on it?
> 
> Frank,
> 
> There is one essential difference between VMWare-like and Xen-based
> solutions. The former is real virtualization and the latter is
> paravirtualization or hardware-based virtualization.
> 
> Using VMWare is easier because it can host almost any operating system
> without dedicated hardware or modifications of OS code.
> According to documentation, Xen solution needs that guest OS is "aware of
> being virtualized" so it requires modification of OS code.
> Or, in order to achieve full virtualizationw and without modifying
> guest OS, Xen requires special hardware features (Intel and AMD
> virtualization features).
> 
> Xen solutions seems to be less universal but hardware specific, so Xen
> performs better. VMWare, Parallels are easier to setup, do not require any
> specific hardware and can run unomidifed guest OS, so they perform
> "slower"
> or require more resources.
> 
> This is my understanding of essential differences between Xen and VMWare.
> 
> Cheers