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Why it is better not to use VirtualBox(VMWare etc..)

Cons

1. VirtualBox can not use full 100% resources of PC. Your hadoop will not be as fast as you expect.

2. You have to start virtual nodes whenever your reboot your PC (unless if you made some auto-start scripts)

3. Several virtual nodes in the same PC can cause mismanagement of resources. If RAM usage of VirtualBox nodes exceeds the maximum then your PC just crashes.


Though, VirtualBox is a good starting point to build experimental hadoop environment.

Pros

1. You can create several nodes in the same PC (if you lack PCs)
2. VirtualBox has Export /Import features that helps you to do "Do once - Copy many" 
3. Do experiments by changing hardware features (add CPUs, reduce RAM etc..)

For learning hadoop VirtualBox can be helpful to build hadoop environment.
However, for production purpose it is better to avoid Virtualbox and use PC itself as a single node.


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