[CentOS] Centos 5.2 and Xen

[Luke S Crawford]

russ at vshift.com writes:
> If you only have 512mb of ram, there's almost no reason to virtualize. Windows needs a minimum of 128-512MB to run stable.  I highly suggest that you get more RAM - its very cheap these days.  

seconded.  my standard server has 8G unbuffered ecc.  Newegg sells 
2x2Gb packs of unbuffered ECC kingston brand ddr2 for under $100.

http://www.newegg.com/Product/Product.aspx?Item=N82E16820134312

No reason, really, to not fill your motherboard with ram.  

> If you want to dedicate a box to virtualization, and won't be using more then 4GB of ram for your virtual machines - I highly recommend xenserver express.  Its free, but has much better performance then vmware.  

the free (closed) xensource product is good... I also wanted to point out 
the new gpl windows pv drivers:

http://wiki.xensource.com/xenwiki/XenWindowsGplPv/

you could use them with the standard open-source Xen, or even with the 
Xen support distributed with CentOS 5, and avoid the ram limits all together.
(well, there is a limit to the open-source xen, but it's ridiculous;  most
of us won't hit it for several years, at least.)  

still kinda beta, but something to watch.  


> I wonder if it can be combined with other technologies - KVM, openVZ, etc to give more then 4GB of ram for virtualization?  I tried installing vmware, but it wouldn't run under.a xen kernel.  

running vmware under a xenU guest wouldn't lift any ram limit imposed by the 
xen kernel or dom0.

the 4Gb limit is added to the free (closed source) citrix xen product
so that people have a reason to pay for the full version...  really,
if you need more than 4G, pay for full xensource, or use the open-source
Xen/open source pv drivers.


I do know some people that run linux vserver guests under a Linux Xen DomU-
that seemed to work ok.

and just for fun, I've run a Xen kernel/Dom0 under a Xen HVM DomU. 
Performance wasn't great;   I don't think I'd do it in production, but
it worked, and was a neat experiment.