Re: [Xen-devel] Remus and Kemari...

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Thu, Jan 21, 2010 at 08:40:35AM -0200, Gilberto Nunes wrote:
> Em Quinta-feira 21 Janeiro 2010, às 08:16:55, você escreveu:
> 
> Hi Pasi
> 
> > On Thu, Jan 21, 2010 at 08:12:21AM -0200, Gilberto Nunes wrote:
> > > Em Quarta-feira 20 Janeiro 2010, às 22:20:17, Brendan Cully escreveu:
> > >
> > > Hi Brendan...
> > >
> > > > On Thursday, 14 January 2010 at 09:52, gilberto nunes wrote:
> > > > > I installed the Remus but had some problems.
> > > > > He leaves the VM very slow. I'm using a partition with DRBD / LVM.
> > > > > May even be that you say that has many layers (DRBD / LVM) that can
> > > > > influence on performance.
> > > > > But the interesting thing is that when Remus is not running the VM is
> > > > > light even with 512M of memory. And look what I'm talking about a
> > > > > Windows 2003 Standard Edition.
> > > > > The Remus to stop working inexplicably (at least for me)
> > > > > and let the VM's started in a state of the two nodes ...
> > > >
> > > > It's taken me a while to get Xen unstable running again, but now that
> > > > I have I can't reproduce any of these problems with an XP guest. It
> > > > remains responsive while Remus is running, and doesn't fail over
> > > > unless I kill it.
> > >
> > > Right
> > >
> > > > Disk access isn't likely to make a huge performance difference
> > > > (although I should say, simply parking a Remus VM on top of DRBD is
> > > > not safe, since there is no way of rolling back changes that have been
> > > > written since the most recent checkpoint).
> > >
> > > What you suggest... NFS!
> > >
> > > > It sounds like your network
> > > > link between the primary and backup is either low capacity or flaky in
> > > > some way, or you have a loaded dom0.
> > >
> > > My network between primary and backup server is a dedicate network, make
> > > with a dedicate fast ethernet switch...
> > 
> > Not sure if Fast Ethernet is enough for Remus syncing?
> 
> Well, I try too with crossover network cable, in Giga Ethernet, but I have 
> the 
> same...
> 
> > 
> > > I do not understand wath you say about that "I have a loaded dom0". On
> > > fact, Xen always have a loaded dom0, right!
> > 
> > I bet he meant "do you have high load on dom0", aka do you have high cpu
> >  usage in dom0? Try running "xm top" to figure out. And also normal "top"
> >  in dom0.
> 
> Ok... I run xm top and get this:
> 
> NAME       
> Domain-0
> 
> STATE 
> -----r
> 
> CPU(sec) 
> 135
> 
> 
> CPU(%)  
> 0.6
> 

So it's not using much CPU.

> MEM(k)  
> 7226368
> 
> MEM(%)
> 86.2
> 

Did you configure dom0_mem= for Xen? 

See:
http://wiki.xensource.com/xenwiki/XenBestPractices

Or is there something in dom0 using all the memory for real? 
Run "top" in dom0, and sort by memory usage by pressing shift+m.


> MAXME(k)
> no limit
> 
> MAXMEM(%)
> n/a
> 
> VCPUS 
> 2
> 
> Something wrong!!!
> 
> >>> I'd recommend using single-processor dom0 and guest to start with, and
> > > > pinning the VCPUs to their own separate physical cores.
> > >
> > > I see. But how I do this!! I am a newbie. If you can point some ways to
> > > me, I'll appreciate...
> > 
> > See:
> > http://wiki.xensource.com/xenwiki/XenCommonProblems
> > 
> > There's a chapter called "How can I limit the number of vcpus my dom0 has?"
> > and "Can I dedicate a cpu core (or cores) only for dom0?"
> 
> I see... However, this procedure do not take alway the beneficity of multi-
> core processors to my VM's!!!!
> 

You can still use multiple cores on your VMs.

If you don't want to dedicate a core only for dom0, at least configure the 
domain weights so that dom0 is guaranteed to get enough CPU time.

-- Pasi


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