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Re: [Xen-users] Few Questions / Application of Xen

  • To: mark.williamson@xxxxxxxxxxxx, xen-users@xxxxxxxxxxxxxxxxxxx
  • From: "Ugo PARSI" <ugo.parsi@xxxxxxxxx>
  • Date: Sat, 25 Mar 2006 16:28:50 +0100
  • Delivery-date: Sat, 25 Mar 2006 15:30:24 +0000
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  • List-id: Xen user discussion <xen-users.lists.xensource.com>

> Currently you need to do this manually. More powerful automatic load
> balancers are likely to appear on the market at some point, as an
> additional management product.

Ok, so you're saying there's currently no solution at all ?
Any opensource project (even beta) that you are aware of ?

Basically, I will need this feature as part of my whole project....so
I'm planning to code my own Xen load balancer... but I would prefer to
help an existing project rather than starting from scratch my own

> Two aspects: for a planned shutdown you'd want the management software to
> live migrate domains off a server you were planning to take down. You'd
> also like it to detect a crash, and reboot the domains on other hosts (and
> lock out the downed server from shared storage so that if it comes back on
> the network any remaining domain images it's running can't confuse the
> situation)

Ok, actually, if you can load balance, it's pretty easy to detect that
a machine is not responding and correctly manage the failure by
sharing the remaining load amongst machines that are alive.
So my question was stupid, sorry :)

> You can change the RAM footprint using xm mem-set (or something like that).
> Again, this is manual but it's possible in principle to script a tool that
> will automatically allocate memory to a domain which is swapping more, and
> revoke memory from domains with low swap activity.

Yeah, I have tried it and it works pretty well.... :)

It's pretty easy to script such a thing when you plan the RAM modification.
Like getting the virtual machine to 128 Megs -> 256 Megs...

But for programs that are quite "memory volatile" it's rather hard...
for example a game server that is growing from 30 Megs to 80 Megs and
that can't stop doing that depending on the number of users....

To add some complexity my main problem is to detect how much RAM is
really needed by the virtual machine, because of the way Linux is
often caching objects in memory, I'm getting a little bit confused...

Any idea on getting all these informations from the Dom0 ?

Thanks a lot,


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