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File-system virtualization use cases and selection criteria

Because ripping out existing file stores and replacing them with a scale-out NAS isn't an option in many situations, file-system virtualization products that aggregate the various file stores into a single global namespace can be viewed as complementary to scale-out and traditional NAS systems, especially during the extended time of transitioning from legacy file stores. "Many customers buy a NAS to get features like replication, archiving and snapshots, but they don't require these for all files," said Brian Gladstein, vice president (VP) of marketing at AutoVirt Inc. "We give them the ability to mix existing low-end file stores with fast filers and provide them with a single namespace."

Even in companies that can centralize their unstructured data onto a NAS with global namespace support, there will likely always be some storage silos that live outside the NAS. It could be departmental data or data that's deemed unworthy to reside on comparatively expensive NAS storage. File-system virtualization products allow combining rogue file stores with NAS devices into a global namespace. A second use case for file-system aggregation is data migration. Acquisitions, storage infrastructure upgrades and data relocation projects are among the reasons for migrating data from one physical location to another. Because file-system aggregation products virtualize access to heterogeneous file stores, they're

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also simple yet effective data migration solutions. Another use case for file-system aggregation is automated storage tiering. Equipped with policy engines for defining data migration rules based on file-system metadata -- such as last access date, file size and file type -- they enable automatic data movement to suitable storage tiers based on defined policies.

File-system virtualization products are available as appliances and software-only products. A software-only product offers the benefits of more flexible deployment on hardware of your choice, and the products usually have a lower degree of vendor lock-in. Conversely, appliance-based file-system virtualization products come in a proven, performance-optimized package and, because hardware and software are provided by the same vendor, there's less risk of finger pointing.

When comparing file-system virtualization products, the level at which virtualization occurs is a relevant evaluation criteria. For instance, while Microsoft Distributed File System (DFS) provides share-level virtualization, a product like F5 Networks Inc.'s ARX series provides file-level virtualization.

Intrusiveness and ease of deployment are also relevant characteristics to consider during a product evaluation. Ideally, a file-system virtualization product should require minimal client changes and the virtualized data on the back-end file stores shouldn't be changed.

File-system support must also be considered. While some systems support only CIFS, products like F5's ARX and EMC Corp.'s Rainfinity support CIFS and NFS, which is relevant in environments with both Windows and Linux file stores. The presence of a policy engine and its capabilities are critical if the product's intended use is for data mobility and automated storage tiering.

This was first published in September 2010

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