NAS gateways support scaling of storage capacity beyond a single standalone NAS appliance. Although NAS appliances have dedicated internal (and in some cases external) modular storage, vendors such as EMC, NetApp and ONStor supply disk-less NAS gateways (also known as NAS heads) that alleviate the need for dedicated storage. This allows Windows administrators to leverage their current investment in SANs for maximum utilization.
The functionality of NAS gateways is identical to that of NAS appliances with dedicated storage; however, each vendor's implementation varies in its degree of interoperability. NAS gateways allow a company to transform existing storage systems into file-sharing and data-sharing platforms which can be accessed via a standard network.
NAS gateways provide another benefit: They allow Windows administrators to share new storage between file-based (NAS) and block-based (SAN) access.
NAS gateways are also an effective way to implement a tiered storage infrastructure, because they enable access to different tiers of SAN-attached storage while providing tiered connectivity for servers. The gateways allow Windows administrators to re-allocate storage capacity across different servers and NAS gateways. This flexibility gives an admin an alternative to having to maintain dedicated pools of physical storage to specific NAS devices or servers.
This means that storage can be utilized more efficiently across different NAS devices and block-attached host servers. For example, if a NAS gateway only needs 5.5 disks and a server needs 5.5 disks, instead of dedicating six disks (rounding up) to NAS and six disks to the server, you could have 11 disks and share the capacity with the 12th disk being a shared hot spare. This is an oversimplification, of course, since it doesn't take into consideration performance sharing or sharing of hot spare disk drives. The fact is that consolidating storage needs across different systems is more efficient and cost-effective than dedicated pools or pockets of storage.
Bottom line: If you have an existing SAN, you may want to consider deploying a NAS gateway to improve storage utilization and enhance your overall return on investment (ROI). By understanding the performance characteristics (I/Os, bandwidth, response time) of target applications, you can determine if you have adequate available network bandwidth to support these and other applications on NAS.
About the author: Greg Schulz is the founder of StorageIO, an analyst research and consulting firm specializing in IT infrastructure. He is also the author of Resilient Storage Networks: Designing Flexible Scalable Data Infrastructures, which is published by Digital Press.
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