Re: [Xen-devel] xen and virtual iron

[Moshe Bar <moshe@xxxxxxxxxxxxx>]

Virtual Iron seems to me to be a mix of Xen and openMosix, combined 
with a Distributed Shared Memory (which openMosix has as an option).
Scaling up applications in a DSM environment is hugely dependent on the 
application. If all you have are HPC type applications, then Virtual 
Iron might scale nicely, but then why would you pay for something which 
stuff like openMosix provides for free? For most business apps, I 
suspect that a DSM-based solution will not scale at all, or have a 
detrimental impact on performance/thruput, due to the issues with true 
and false sharing.
They do have a pretty console application, though.

Moshe





On Feb 16, 2005, at 7:57 AM, Andrew Theurer wrote:

> Sean Harper wrote:
>
> > At Linuxworld a company called Virtual Iron is demoing a product that,
> > like Xen or VMWare, can break physical machines into virtual machines.
> >
> > However, unlike Xen or VMWare, this product can also aggregate 
> > physical
> > machines into virtual machines.  In other words, it is possible for 
> > the
> > user to specify that 3.5 cpus from 2 machines (2 from 1 and 1.5 from
> > another) be assigned to a virtual machine. When linux boots on that
> > virtual machine it simply looks like a 4 cpu machine (but 1 of the 
> > cpus
> > is slower). Presumably there is a pretty big performance penalty for
> > sharing across machines, which they mitigate to some extent by 
> > requiring
> > Infiniband.
> >
> > It seems like most of the tricky work is around caching to optimize 
> > the
> > performance across the slower communication bus (when sharing between
> > machines).
> Hmm, sounds like a NUMA system, with a relatively low throughput and 
> high latency interconnect.   Not sure if anyone would want to do this 
> on a workload where performance matters.
> I suppose with a layer of abstraction like Xen, doing something like 
> this is feasible.  You could leverage the NUMA code in the linux 
> kernel, but I would think you would need a very highly parallel 
> workload to make this effective, and if you have that, a cluster setup 
> would probably work just as well anyway.
> -Andrew Theurer
>
>
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