[CentOS-virt] Virtualisation, guests cached memory and density

Fri Feb 8 19:45:34 UTC 2013
Steve Thompson <smt at vgersoft.com>

On Fri, 8 Feb 2013, James Hogarth wrote:

> Have you looked at KVM with a c6 host yet? It's a marked improvement over
> c5 hosts...

Yes, I have a samba4 domain controller running as a KVM guest on a CentOS 
6.3 host (two of them w/DRS, actually). Runs like a champ.

I also have two LVS-DR load balancers running as CentOS 6.3 KVM guests 
with keepalived w/VRRP, one on a C5.8 host and one on a C6.3 host. Each 
guest has three network interfaces, as does the host (bridged mode with 
dual bonded interfaces underneath). Services are LDAP, Windows remote 
desktop, HTTP, webmail, IMAP and SMTP. Everything works fine for all 
services with the exception of SMTP, which works fine on C5 but not on C6 
(same guest setup, same realservers), where it loses connections when 
sending mail messages larger than about 10MB. Even setting rp_filter=2 
does not help; I have not pinned this one down yet, but I doubt that KVM 
is responsible since C5 works.

As a point of interest, the Windows RDP service feeds 31 Windows XP virtio 
realservers, which are themselves KVM guests on a Dell R710 (8 physical 
cores + hyperthreading, 48GB) running CentOS 5.9 (soon to be 6.3). Runs 
most excellently.