[Devel] Re: [Vserver] VServer vs OpenVZ

[Kirill Korotaev]

> 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.
I suppose OpenVZ can do the same :) if you like debugging :)

> 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).
this is not true! Fairscheduler in current implementation on 2.6 kernel 
is O(1) and doesn't depend on number of processes anyhow!
And we are working on improving it much more and implement some 
additional features in it.

> 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.
Mmm, if you are an SWsoft customer you can always request some netfilter 
module to be virtualized. It's a matter of couple of days actually... 
And there are no any problems with it. We just virtualized the basic set 
of iptable matches and targets and those which are rarely used didn't.

There were only 4(!) IPv6 requests during 2 years. It's the same as 
netfilters - no much demand, no feature.

> 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)).
not sure what you mean... memory caching?! it is not true again then...

> 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.
RSS is good yeah, but there are lot's of DoS possible if you limit RSS 
only. No lowmem, no TCP bufs, etc... I personally know many ways of 
DoSing of other resources, but if you don't care security this is 
probably ok.

> 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
Glad to hear that.

> So which is better?  Neither, it depends what the user requires and what 
> they are willing and wanting to do.
> 
> My 2 cents..
thanks for a lot of information!

Kirill