[Linux-cluster] Hardware recommendation

[Ahmed Taha]

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).

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.

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,



On Fri, Jul 24, 2009 at 5:54 PM, Paras pradhan <pradhanparas at 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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