Subject: Re: [vserver] VServer vs OpenVZ.
From: Gordan Bobic <gordan@bobich.net>
Date: Thu, 09 Dec 2010 19:31:58 +0000

On 12/09/2010 06:14 PM, mourad.alia@orange-ftgroup.com wrote:
> Dear VServers,
>
> As introduced in my previsous post, wa are about using VServer to emaulate P2P like
VoIP peers. This is used for sacalability and performance testing of our VoIP application.
>
> Here are our needs :
>
> A) We want to have a maximum of VMs per server. Our server are 24 hyperthreded machine
with 6 physical network interfaces :
>      IP Network Server NSN2U (Ballenger-NH)
>      Single 600W AC PSU
>      Memory 24 GB
>      CPU Dual Xeon E5645
>      SATA HDD 500GB
>      Ethernet I/O Module (four Gigabit rear ports)
>
> B) Each VM hosts a JVM which run one or many instances of our applications.
>
> C) The applications (VoIP peers) communicate basically through multicast.
>
> D) Each n VMs (m applications) will use one given Eth physical interface to distribute
correctly the network traffic.
>
> Currently, there is a hot discussion in my departement on OpenVZ vs VServer : " VServer
is more tooled, simpler, virtualise the network, supports hot VM migration".

AFAIK, vserver doesn't support live/hot migration of VMs. Do you really 
need it, though? Startup time on my VMs (based on RHEL6) is on the order 
of 5s for the complete system including services (mysql, apache, etc.).

> What do you think about this versus ?
>
> Any particular advise towards my use case ?

The absolute killer feature of vservers for me is hashify. In a 
nutshell, it adds a feature to provide copy-on-write hard-links, which 
means that once you have hashified your guests, all the DLLs have the 
same inode number and mmap into the same memory. That means that if you 
have 100 guests running the same base setup, you don't have 100 
instances of glibc wasting RAM, but only one. On top of that, since 
identical files are hard-linked, it makes the cache efficiency much 
greater. This means you can overbook your memory way, way more than you 
otherwise could and gain some performance at the same time.

Gordan