In keeping with the purpose of using virtualization technology the data storage solution must also be resilient and dynamic. Options in tasking and deploying storage for a virtual machine must follow suit with the core technology. Your choice for data storage needs to have high availability and fault tolerance for optimal uptime. Access to the data needs to be fast so as not to affect the performance of the virtual machine. Optimally, the data storage should be easily expandable without creating additional volumes.

The storage technology used and its method of access typically determines if all or parts of the objectives are met and if so, to what degree.

The practice of data storage on the same hardware as the virtual machine is strictly taboo as it defeats the purpose of deploying virtualization in the first place. Virtualization data storage is usually accomplished with Network Attached Storage (NAS) or a Storage Area Network (SAN). Both forms of storage have their benefits and drawbacks as will be explained later in this article.

A NAS – or Network Attached Storage comes in the form of a hardware device that usually contains one or more arrays of hard disks handled by one or more controllers. The advantage of having multiple controllers is that in the case one fails the other may take over the failed controllers RAID array, often in a somewhat performance deprecated state but none the less still operational. NAS devices come with an operating system that is meant to control the storage functions needed and provide device setup and management access in the form of secure shell access or VIA a web browser.  NAS uses common file based protocols to allow access to storage with NFS being popular for UNIX systems and CIFS for windows systems.

A SAN – or Storage Area Network is a high speed network of interconnected data storage devices. The storage devices connected can be of different brands. SAN’s are commonly used in somewhat larger storage implementations than NAS due to their cost and complexity, although they can encompass NAS devices. The drawbacks of using a SAN as compared to NAS are cost, and more complex administration.

Another difference between the two storage options is that with NAS you use file level operations and SAN’s uses Block level I/O.

Using network storage for your virtual machines there is always the concern of latency. This problem is being overcome with the use of TOE (TCP Offload Engine) enabled network cards and faster fiber channel and copper interconnects.

Your choice of virtual machine data storage ultimately should depend on the size and demands of your virtualization deployment scenario and of course budget.