One method to aggregate multiple NAS devices into a single, abstracted entity is with NAS virtualization. In its simplest definition, NAS virtualization is using some means to present multiple NAS devices as a single NAS. The customer ideal is that heterogeneous NAS devices can be aggregated to provide a superset of the benefits that individual NAS devices provide.
There are different approaches to achieving NAS virtualization, and each have slightly different characteristics. In general, the approaches include putting another device in front of the NAS devices that will provide a single connection as "networked attached storage." The "front-end" connection point has several variations, but aggregates the different NAS devices connected as a single image. The front end may be a special switch, an "appliance" -- which is a server with special software -- or a custom hardware product.
Another approach is to add software to existing NAS devices to cluster them together in some fashion. Usually, the implementations only work with devices from the same vendor. The clustering software may not be similar to the server clustering software commonly available, but does provide additional capabilities over single NAS systems.
Each vendor's products vary in some fashion and some implementations may have advantages over others in specific areas. The different implementations warrant investigation and consideration.
There are many general benefits to NAS virtualization that can be highlighted without getting into specific implementation benefits.
- Capacity utilization -- rather than have excess capacity in some devices and be out of space on others, the entire capacity is available with distribution of data.
- Load balancing -- activity can be redistributed across multiple NAS devices to get the greatest performance for the given configuration.
- Global namespace -- based on the definition of the file systems and namespaces, a global namespace where files that span multiple NAS devices, whether local or remote, can be presented as a single namespace for access.
- Data movement -- files may be moved transparently to redistribute data either for load balancing, capacity utilization, data protection, addition of additional NAS devices (for capacity or performance reasons) or for some tiering of storage.
Rarely does something come for free. It is no different with NAS virtualization, whether it is buying a specialized device or software to run on an appliance or the extra cost for clustering software of some type. Cost is just one consideration, however. There are some other things that must be considered, as well, to see if they are issues with the implementation.
- Complexity -- virtualization will probably introduce some additional complexity. How complex depends on the implementation but it will not be as simple as a single NAS device.
- Heterogeneity -- some NAS virtualization solutions will work across any NAS devices while others may be limited.
- Administration -- individual NAS devices (certainly those from different vendors) may need to be managed independently in addition to managing the virtualization.
- Support -- with elements from different vendors, problem resolution may start with a conference call and some serious finger pointing.
- Advanced function implementation -- the use of remote replication and point-in-time copy functions may be different than from a single NAS device, and use of those functions on individual NAS devices may not be possible.
- Familiarity -- some of the implementations may be relatively new and there may be a lack of familiarity by many.
Decisions -- Based on situation
NAS virtualization provides significant value in scaling into larger storage environments. Choosing to purchase and implement NAS virtualization should be based on individual requirements and an evaluation of the merits of each offering.
About the author: Randy Kerns is an independent storage consultant. In the past, he served as vice president of strategy and planning for storage at Sun Microsystems Inc., and covers storage and storage management software including SAN and NAS analysis.
This was first published in February 2007