Good question.

It's hard to put an exact number on it because of the different types of resources that can be made available(vm,bare-metal,lab machines), but we should be able to get theoretically close.

Correct - multiple management nodes is an important part of the scaling. So the first question is how many resources can a single management node support.

Additional things to consider are how the nodes get provisioned and the usage profile(asynchronous or synchronous). Also this is assuming one has robust web server, database, networking, storage and management nodes. The network, storage and management nodes are a big factor.

Provisioning options -
bare-metal vs. hypervised vs. stand-alone lab machines

*bare-metal - installing an image to disk using xCAT:
typically we have experienced anywhere from 150-200 blades per management node for asynchronous use.

*hypervisor using vmware free server vs ESX/i with either persistent vs non-persistent mode.

VMware ESX with network datastores for the vms and running in "non-persistent" mode. One could probably get 1000+ vms per management node maybe more. Again this assumes fast access/networking to storage (10G ethernet or fibre), a nice storage array and running 20+ vms per esx server.

vmware free server - typically 5-10 vms per server

*stand-alone machines:
at NCSU we also use traditional lab machines when the university labs close. This mode is only brokering remote access to nodes, therefore no loading is going on. One could probably get 700+ machines per management node.

Usage Profile: asynchronous vs synchronous
synchronous usage is the most demanding usage, block allocations/provisioning for a class, workshop or some other event that needs many nodes at a single event.

asynchronous usage - users independently request nodes at any given time. This is spread out over time and has a lower provisioning load on the management node/s.

Since we(ncsu) don't have the infrastructure to confirm these numbers this is just an educated guess based on past experiences based on what we do have. I would feel comfortable saying that if using multiple management nodes and an ideal HW setup, beefy blades (multi-core, extended memory blades, high-end storage, fat-pipes, etc), vcl could conservatively support several thousands nodes.


--On September 10, 2009 12:20:39 AM +1000 Sengor <> wrote:

Hi Brian,

I'm not certain of the exact numerics, however I do believe support for
multiple management nodes (vcld's) is an intentional scale-out approach.

Perhaps some of the guys @ NCSU know this one, I believe their VCL
instance is currently the largest one in production.

On Wed, Sep 9, 2009 at 11:55 PM, Brian Bouterse <>

Hi All,

I'm wondering what the scalability limits of VCL?  What are the limits of
the vcld component, and why do we believe they exist?  Does the frontend
have any scalability limits?

I'm trying to figure out what the reasonable number of VMs a single vcld
installation can concurrently support.  What do you think and why?


Brian Bouterse
NEXT Services


Aaron Peeler
OIT Advanced Computing
College of Engineering-NCSU

Reply via email to