Can my servers hold the load?

[ServerTech2011]

Hello everyone. This is my first post so I apologize if this post is a bit off-topic, though it includes cPanel in it.
I plan on getting RackSpace Cloud Servers [For their reputation, awesome support and 100% uptime SLAs], installing cPanel/WHM and CloudLinux on it [And a few addons] and selling shared hosting while being on the cloud. Maybe we can refer to this as Cloud Hosting, or Cloud Shared Hosting.

Now, my question basically is whether these servers can hold the number of websites I'm planning to host on each server. Since RackSpace limits Disk Space and I can't upgrade Disk Space only, I'm limited to providing only about 5GB of disk space per instance and 10GB of disk space per enterprise instance.

I plan on selling these hosting solutions as 'instances'. I also plan on creating two completely isolated environments, which I refer to as Personal and Enterprise environments. The difference between these two isolated environments is the number of instances running on the same amount of available resources.

My initial basic configuration to start off with is with 5 servers and the following configurations for each:

Server 1: 2GB RAM Linux Cloud Server [CloudLinux + cPanel/WHM + Addons]
This server is for the personal environment. This environment will run 12 instances (1 instance per customer, though clients may buy more than 1 instance) per 2GB of RAM allocated. The personal environment has more instances because personal websites have lower traffic requirements and therefore lower resource requirements. This server comes with 80GB Disk Space. 10GB of this space will be reserved for cPanel/WHM + Addons + OS.

Server 2: 2GB RAM Linux Cloud Server [CloudLinux + cPanel/WHM + Addons]
This server is for the enterprise environment. This environment will run only 6 instances per 2GB of RAM allocated. This doubles the resources allocated per instance. Since this environment is on another server, it is isolated from the personal. This server comes with 80GB Disk Space. 10GB of this space will be reserved for cPanel/WHM + Addons + OS.

Server 3: 2GB RAM Linux Cloud Server [CentOS 5.x - 6.x + MySQL]
This server is the primary database server which will serve both Server 1 and Server 2. This server too comes with 80GB of Disk Space. I don't really need to reserve disk space because the base MySQL installation would not be utilizing much Disk Space. The remaining will act as database space available to both environments.

Server 4: 256MB RAM Linux Cloud Server [CentOS 5.x - 6.x + cPanel DNSonly]
This server acts as the first DNS server. This server comes with 10GB of Disk Space.

Server 5: 256MB RAM Linux Cloud Server [CentOS 5.x - 6.x + cPanel DNSonly]
This server acts as the second DNS server. This server comes with 10GB of Disk Space.

This is the basic starting configuration for the service I'll be providing.
Since this is hosted in the cloud, I'll be scaling up these servers as certain loads are reached.

Now what I you all is to assure me that hopefully this configuration will work out comfortably without any issues and the number of instances I've mentioned can actually be held by these servers. I also need to know if the DNS servers will be fine with 256MB RAM servers.

Additional Info: RackSpace does not monitor CPU Usage. For every linux server I buy, I get a certain share of the quad core AMD processors RackSpace utilizes. RackSpace provides a certain guaranteed amount of CPU depending on the size of the server, and also allows unlimited CPU bursts depending on availability of extra CPU cycles.

Since I have CloudLinux, it might help me from users using too much resources without buying enough instances for the same. Hopefully, everything works out well.

What I'm worried for is that I provide a 100% uptime SLA and promise perfect website speed. Since I'm not those hosts who promise stuff and don't provide it, I need to be sure the instances won't slow down the server.

Basically, on the personal platform, I plan to run 6 instances per GB of RAM and on the enterprise platform, 3 instances per GB of RAM.

So, please help me here and provide me advice on the probability of this configuration working well and I apologize once again if this post is a little off topic.

[GIANT_CRAB]

Hello,

Specifications of the cloud, like processor speed (Ghz), etc.

Also, is your hosting managed by you or managed by the host?

Btw, a 64 bit OS is required to support more than 4GB of RAM.

I look forward to your reply.

Yours truly,
GIANT_CRAB

[ckh]

With a PAE enabled kernel you can access of up to 64 GB of memory on 32-bit machines.

[ServerTech2011]

Hello,

Specifications of the cloud, like processor speed (Ghz), etc.

Also, is your hosting managed by you or managed by the host?

Btw, a 64 bit OS is required to support more than 4GB of RAM.

I look forward to your reply.

Yours truly,
GIANT_CRAB

RackSpace does not monitor CPU usage. I can burst upto any amount available on the host machine. For a 2GB machine, I have a share of 4 vCores. I have set up a near failproof 8 month plan to be able to reach a configuration of 2x 30GB webservers (8 vCores each [Dedicated]) + 1x 15GB MySQL server (4 vCores [Dedicated]) + 2x 512MB DNS servers. Oh and it's completely managed by me. And yes a 64 bit OS. I'm not going to use x86 architecture anywhere.