In this post we will look at the VMware software, specifically vSphere 5.5. This software can be broken down as follows:
- Virtual Machines concepts
- ESXi Hypervisor
- vCenter and its features
- Storage and Virtual Networking
- vCenter Operations Manager
- vCenter Configuration Manager
- vCenter Site Recovery Manager
1. Virtual Machine Concepts
So just what is a virtual machine?
- Looks like a physical server to the user
- Users can’t tell the difference
- Virtual but dedicated hardware for each OS instance
The advantages of virtual hardware are:
- Replace and upgrade (hardware) on the fly – no service interruption
- Add new devices without rebooting
- Stable and dependable
- No need for OS modifications
Using the vSphere web client we can manage servers remotely, including OS installs from CD/DVDs or ISO images.
What can we do with a virtual Machine?
Given that a virtual machine behaves just like a physical machine, we can almost anything a physical machine can do including:
- File Server
- Data base server
- Email server
- Applications server
- and many other server types or applications
So why are we so interested in virtual servers? There are a number of reasons why we might consider running virtual servers:
- Consolidate a number of lightly used servers – to conserve space and power
- Protect against hardware failures/site disaster – VMs are easy and quick to copy, backup and replicate
- Ease of provisioning servers – quick to set up and deploy new servers
There are some things that virtual machines can do that a physical machine cannot do.
Snapshots are images of the running virtual server. They can be used to ‘roll back’ any issues or problems with the server; perhaps caused by a bad driver update or patch. This can be achieved in minutes, as opposed to a complete server rebuild, which can take hours.
It is important to note that snapshots are NOT backups of the server. For a complete backup, we use the Image backup. This is a similar process that allows for backup of the entire ‘metal level’ of the server, and allows for file based restore.
Both of these types of backup have another advantage in that the VM is not tied to specific hardware. In the event of disaster, you may not have access to specific pieces of hardware, so having VMs means that you can recover from disaster on what ever hardware you have available if necessary.
In addition, we can add server resources (like memory, disk space and CPUs) with a reboot. With a traditional hardware server, it must be shut down and the case opened to add resources, but with a virtual machine, we can simply allocate more resources simply, and without having to reboot. This means that maintenance can be done on the fly.
2. The ESXi Hypervisor
As we mentioned previously, the hypervisor is the resource allocation system that interfaces the virtual machines to the underlying hardware. The hypervisor is also our management system to control the VMs. We issue instructions to the Hypervisor that control the machines and the resources allocated to them.
Before we go any further, it should be noted that there are two types of hypervisor:
- Type 1 -Bare Metal
- Type 2 – Hosted
In this course we are focusing on the type 1 – bare metal. This means the Hypervisor is installed directly to the server without an operating system and OS’s are installed on the virtual machines. In the case of WMware, this is the ESXi Hypervisor.
The type 2 – hosted hypervisor is the type I have on my iMac (I’m running Xubuntu Linux 12.04 with Oracle’s Virtual box) and I use it to run a number of headless Linux server instances and for those legacy programs (read old games) I run windows 98, XP and Win7 as well as an instance of Server 2003 R2 – but not all at the same time! The VMware hosted hypervisor is VMware Workstation.
Bare metal types are the preferred type for data center installations, as they are not dependent on a host OS and generally consume less machine resource. Hosted types are generally used in simple installs for legacy software support etc on a users workstation, rather than a server (except maybe in SOHO applications where cost is more of an issue than performance.
ESXi can be installed from CD/DVD direct to the target server hard drive(s) but also to SD cards, flash cards and USB drives. It can also network boot PXE and TFTP servers.
Using the ESXi Hypervisor, we can:
- create virtual machines
- adjust virtual machine configurations
- monitor performance
- configure and patch hosts
… which is great if we have only one piece of hardware running ESXI with some VMs. However, if we have multiple servers, hosting multiple VMs, we need a better way to centrally manage them. This is where vCenter comes in.