Virtualized servers are often presented as having an excellent – or even stellar – ROI for businesses. While this is true on paper because virtual machines eliminate the need for physical servers, constant maintenance and a separate server for each OS, there it does not represent the whole truth. There are a number of problems presented by VPS storage that can negatively affect the return on a virtualized environment.
The single most difficult problem a company can encounter when using a virtualized system is referred to as the "I/O Blender." Companies using virtualized systems often find that its physical storage performance greatly outperforms its virtual. Sometimes this difference can be as great as 80%. It is here that the “I/O Blender” problem arises: because a virtual server is doing the work of multiple servers each with their own I/O stream, rewriting and storage of data happens in a very random pattern, causing general slowdown to the machine.
One proposed solution is to create disk-based log space dedicated to each virtual host. This allows data rewriting to happen serially and with optimized algorithms, helping limit the overall server randomness. Once a server has such a solution installed, the data rewrites are able to occur at the maximum speed of the disk technology used, giving a performance boost of up to 80%.
While virtual servers are unquestionably moving into the mainstream of application technology, storage issues continue to be the area of greatest concern, thereby requiring extensive attention.
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