If you are going to have relatively balanced storage needs between the two service types (SAN and NAS) then it makes sense to look at unified storage. Unified storage implies that it will simplify storage management by having a single platform to deploy storage services (NAS or SAN) from. The area to look at in unified storage is how well the two services are integrated and does that really make it easier for you? Companies like SUN, NetApp, ONStor and Nexenta have all done a good job in providing a relatively smooth user experience.
Presenting unified storage as easier to use implies that managing two separate storage platforms is inherently harder. Many SAN systems are very easy to use now as are most NAS systems. Unless you are looking to unified storage as your first step into shared storage or if you have shared storage you can replace most of it with a unified solution, I don't see an inherent gain in ease of use by a unified system. While ease of use is there, it is also there in modern SAN or NAS only systems, so don't judge unified storage by ease of use alone. There is more to it.
The second area to look at is to make sure the unified system can sustain your performance requirements. If you are going to have a need to provide both SAN and NAS equally and have relatively modest performance requirements then the simplicity of the single platform may work in your favor. Understanding the performance requirements is critical. Many unified vendors also offer non-unified block focused storage systems for a reason, to address customers that need the higher-end performance of pure block based fibre channel SAN storage. Make sure you are comfortable with both the block I/O and file I/O performance of the unified system.
As always there are exceptions, and some vendors will claim that their unified block I/O performs as well as a non-unified block I/O system and it may be for your environment, just test it.
There comes a time when a focused storage system that specializes on block I/O or file I/O is a better fit. This can occur when your environment becomes heavily saturated with one of those storage services (SAN or NAS) and especially when there are immediate performance issues or long term scalability concerns. Companies like 3PAR and Isilon have made their mark by offering storage solutions that are designed to address performance and scalability while at the same time maintaining ease of use. As we discuss in our article "Searching for High Performance Storage" the need for high performance storage I/O is no longer limited to the lunatic fringe. Even SSD systems like those from Texas Memory or Violin Memory can be considered, non-unified storage and are clearly focused on solving a storage performance bottleneck.
The final area to explore with unified storage is to see if there is a significant cost savings. Basically can you deploy a single system that meets your performance demands and your storage services need at significantly lower price point? Especially in the mid-sized market this may be unified storage's key advantage. Most mid-sized organization simply can not muster the storage I/O performance to push todays storage systems anywhere close to their limits. It is simply more economical to have a single storage system do more than one task, potentially providing unified storage solutions a price advantage in this market.
To net it out, unified storage should be considered if you have mainstream performance requirements, a fairly balanced need of NAS and SAN services and if there is a compelling price advantage.
In our next entry we will explore another form of unified storage; virtualization appliances that can manage and unify multiple vendors storage hardware.
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George Crump is founder of Storage Switzerland, an analyst firm focused on the virtualization and storage marketplaces. It provides strategic consulting and analysis to storage users, suppliers, and integrators. An industry veteran of more than 25 years, Crump has held engineering and sales positions at various IT industry manufacturers and integrators. Prior to Storage Switzerland, he was CTO at one of the nation's largest integrators.