[Users] Switching from VMWare to OpenVZ?

[Tim Small]

On 12/04/11 23:37, lists at yhmail.de wrote:
> Hello everybody,
>
> my workgroup and me do mostly simulations of complex organic compounds
> and java programming. Since most of our programms run pretty unstable
> we have been using VMWare to virtualize our Servers (Intel i7-920
> Quad-Core/24GB DDR3 RAM/4TB RAID5).
>
> A few months ago a colleague of mine tried OpenVZ and had a lot of
> troubles setting it up.
> I think the most confusing part for him was the RAM/Swap-Management.
> So I thought before we try it again, we might just ask others if they
> have a similar setup.
>
> Currently we have 4 VM with 5 GB RAM/15GB Swap each. Since there is a
> lot calculation involved it is always hard to say how much memory will
> actually be used.
>
> With OpenVZ we got the error "out of swap/memory" a lot.
>
> What kind of settings, limits would you recommend with OpenVZ for that
> particular setup?

Dunno, it depends on how worried you are about one job potentially
taking out the whole server, and what the likelihood is of multiple VMs
all using a lot of RAM at the same time.  If you are using Debian then
maybe use

vzsplit -n 1

or

vzsplit -n 2

or interpolate somewhere in between?  The "vzcalc" tool is also worth
looking at, and I'd advise using Munin on the machine to track resource
usage (there are a couple of OpenVZ plugins).

It's also worth noting that 2.6.26 isn't a kernel version that OpenVZ 
support, where as 2.6.32 (as used by Debian 6.0) is an OpenVZ supported
version, so you may want to switch to that before doing a new deployment.

In particular if you are using software RAID5, I've seen some IO
deadlocks on 2.6.26 with OpenVZ and software RAID - those problems
aren't present on 2.6.32.

Also worth noting is that I don't believe OpenVZ is planned to be
officially supported in the next Debian version (possibly it will be if
Linux Containers - LXC - aren't workable).

Cheers,

Tim.