[Devel] Re: [Vserver] VServer vs OpenVZ

[Matt Ayres]

Eugen Leitl wrote:
> Before I try OpenVZ I would like to hear comments of people
> who've ran both VServer and OpenVZ, preferrably on the same
> hardware, on how both compare. 
> 
> Factors of interest are stability, Debian support, 
> hardware utilization, documentation and community support,
> security.
> 

As the owner of one of the larger VPS providers around we do use 
Virtuozzo (commercial support, less work packaging, etc) although I am a 
big fan of the VServer project.

For a hosting service I'd have to recommend Virtuozzo over either, as is 
a large purpose of OpenVZ I believe :)  If you feel you can do the work 
to keep track of kernel changes, participate actively in debugging, etc 
then VServer would be fine.

As far as the technical debate between the projects, I have more 
interest in inputting on that.

1) "Fair scheduling" - as far as I can tell the VZ "fair scheduler" does 
nothing the VServer QoS/Limit system does.  If anything, the VZ fair 
scheduler is not yet O(1) which is a big negative.  VServer is built on 
standard kernel and therefore uses the O(1) scheduler (an absolute must 
when you have so many processes running on a single kernel).

2) Networking - The VZ venet0 is not perfect (no IPv6, still limited 
iptables, etc), but it still allows a lot more to be performed than 
VServer in the networking arena.

3) Disk/memory sharing - OpenVZ has nothing.  Virtuozzo uses an overlay 
fs "vzfs".  The templates are good for an enterprise environment, but 
really prove useless in a hosting environment.  vzfs is overlay and 
therefore suffers from double caching (it caches both files in 
/vz/private (backing) and /vz/root (mount)).  VServer uses CoW links 
which are modified hard links and eliminates the double caching. The 
Vserver vunify program (to re-link identical files due to user upgrading 
to same RPM's across VPS's, etc) takes a few minutes to run.  The 
Virtuozzo vzcache program to do the same can take 2+ days to run on a 
host with 60+ VPS's.

4) In most other areas OpenVZ and VServer are similar.  OpenVZ has many 
UBC's, but since most oversell some such as vmguarpages really have no 
affect.  Vserver limits the major memory limits (with RSS being a key 
one that OpenVZ cannot do).  On the flip side OpenVZ can limit lowmem 
(kmemsize) while VServer cannot.

5) Quota inside VPS - The new way of linking the quota user/group files 
to /proc in OpenVZ is very good (genius?) idea I think.  Currently I'm 
not even 100% sure quota-inside-VPS works under VServer, it's been a few 
months since I've experimented with it or talked to Herbert.

So which is better?  Neither, it depends what the user requires and what 
they are willing and wanting to do.

My 2 cents..

Thanks,
Matt Ayres