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Re: [Linux-cluster] Hardware recommendation

Thanks Ahmed for your reply.

On Tue, Jul 28, 2009 at 7:16 PM, Ahmed Taha<consult itlinux gmail com> wrote:
> Hi,
> Dell PowerEdge is a good choice. I would go for the PowerEdge 2850 if I
> could.  For such a number of virtual machines (30), you will definitely need
> not only high RAM but CPU power as well. First, let us consider the memory.
> Each RHEL5 guest instance needs at least 512M (eventhough I have tested few
> instances and I was able, with some tuning, to make it work down to 384M,
> but definitely not 256M). The same min of 512M for Solaris10 will be
> essential. Now for 30 VMs, you are talking about 15G of physical memory (not
> including page cache and buffers).
Are you talking about fully virt VMs or Para Virt in this case? WIth
Para Virt the allocation is dynamic. Isn't it?

> For CPUs, theoretically, performance hit starts when the number of VCPUs
> goes above the number of physical CPUs, but the exact nonlinear behavior has
> a lot of debate about it. What I have actually tested is two AMD64 dual-core
> (4 cpu's) while I was able to build up 18 VM's with one VCPU per each,
> however, performance was very bad. I repeated the experiment on just one
> Intel dual-core processor (2 cpu's) and I was able to build up to 10 VM's.
> But once again, I could not run except 4 or 5 with a production-level
> performance. So, you may scale accordingly for these 30 machines. I would go
> for 4 dual-core or two quad-core at the least.

If I understand correctly, to get a production level performance even
with 2 quad core, I can run only around 8 virtual machines?

> Don't forget dom0 may be picky about how much memory it gets, specially if
> you will run X. Check the forums for further discussions if you encountered
> X issues when xend starts.
> Hope this helps,

Thanks !

> On Fri, Jul 24, 2009 at 5:54 PM, Paras pradhan <pradhanparas gmail com>
> wrote:
>> hi,
>> I will be creating a cluster using red hat EL 5.3 consisting of 3
>> nodes which will run Xen virtual machines. The first two nodes will
>> host around 30 virtual machines ( all paravirt Linux and some Solaris
>> if possible) . The third node will be basically a fail over node and
>> will host virtual machines if there is a problem at node 1 or node 2.
>> I do not know if this is the right way to ask but I need
>> recommendation on which CPU to choose (i7, phenom, quad core or dual
>> core) and how much RAM do I need on node 1 and node 2 and on also node
>> 3. And also which server hardware is recommended for my purpose. My
>> test cluster is based on Dell Poweredge 1800 machines with DRAC 4
>> (which I am using for fencing) and looks like DELL Poweregde server
>> can be a good candidate.
>> Any help is highly appreciated.
>> Thanks
>> Paras.
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> --
> Ahmed G. Taha
> Linux Systems Consultant RHCE &
> Operating System Programmer
> (Cell): (573) 289-7300
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