Advantages of Server virtualization
1. Lower number of physical servers - you can reduce hardware maintenance costs because of a lower number of physical servers.
2. By implementing a server consolidation strategy, you can increase the space utilization efficiency in your data center.
3. By having each application within its own "virtual server" you can prevent one application from impacting another application when upgrades or changes are made.
4. You can develop a standard virtual server build that can be easily duplicated which will speed up server deployment.
5. You can deploy multiple operating system technologies on a single hardware platform (i.e. Windows Server 2003, Linux, Windows 2000, etc).
Disadvantages of Server virtualization
Magnified physical failures
Imagine you have ten important servers running on one physical host and its RAID controller runs amok, wiping out all of your hard disks. Don’t say that this is not very likely, as we have already had two or three incidents from malfunctioning RAID controllers from well-known brands
There are several ways to compensate for this downside. One is clustering, which certainly entails extra efforts. Another answer is to backup the virtual machines with a CDP (Continuous Data Protection) solution.
If your physical server goes down, it is possible to restore all VMs quickly to another host. This solution implies that you have enough capacity left on another host. Thus, if your virtual infrastructure is well planned, physical failures may be less problematic. However, this means that you have to invest in redundant hardware, which more or less eliminates one of the alleged advantages of server virtualization.
Disadvantages of Server virtualization
There is no doubt that virtualization requires extra hardware resources. The problem is that it is almost impossible to estimate in advance how many extra resources will be needed (Extra cost to business). I know that there are capacity planning guides and tools but from my experience every piece of software behaves differently in a virtualized environment. We have applications that are quite modest as long as they run on a physical server, but when they were virtualzed their resource requirement multiplied
It sounds so easy – install a virtualization solution and then just deploy your servers as you are used to. Not really! Many things are different in a virtual environment. I will give you just one example. When we installed our first server virtualization solution, I instructed our administrators to test some of their servers in the virtual environment.
After a week or so, an administrator told me that he could not test his server because there was no more RAM available on the host. I was quite surprised, as this server has enough capacity for 10 VMs.
Complex root cause analysis
Virtualizing a server certainly implies big changes to the whole system. A new layer of complexity is added and can cause new problems. However, the main difficulty is that if something doesn’t work as it is supposed to, it can require considerable extra efforts to find the cause of the problem. I have another example for this downside of server virtualization.
New management tools
Virtualization also has advantages, such as easier migration, cloning or snapshots. However, you can only take advantage of these new capabilities if you have the proper tools. Often, the tools that come with a virtualization solution are not enough, only supporting basic management tasks. This means that you need additional utilities, which cost both money and time. I am not only talking about such tools as VMware Virtual Center or Microsoft Virtual Machine Manager (VMM).
Virtual machine sprawl
Even though virtual server management can get quite complex, installing a new virtual machine is a piece of cake. You need a new server? Just clone your master image to a new VM and you are done within a few seconds. The problem is that the number of servers might grow faster than the number of admins who are supposed to manage them. It is good that even virtual servers have physical limits. As soon as you reach the limit of your virtual capacity, the virtual machine sprawl will naturally stop.