Get control of NAS systems


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2. File virtualization systems

File virtualization systems separate the physical location of a file from the representation of that file. File virtualization systems essentially eliminate the requirement for a user or application to know exactly where their files are stored as they see only a single global namespace (GNS.) Depending on how it's implemented, file virtualization allows transparent file access, load balancing, data storage tiering, file migration, and even snapshots and replication for multiple homogeneous or heterogeneous NAS systems.

File virtualization implementations can usually leverage Microsoft's DFS and/or Linux/Unix automounters by acting as a management layer. This allows them to automatically update the DFS Namespace to include NAS filers and file servers, while also providing common management for multiple dissimilar NAS systems. F5 Network Inc.'s ARX file virtualization appliance also provides available disk space monitoring, while others (Avere Systems Inc.'s FXT Series and EMC Corp.'s Celerra NS with FAST) provide storage tiering.

No additional software is required to leverage DFS Namespace and Linux/Unix automounters. If the file virtualization technology fails, the file maps for Windows and mounts for Linux/Unix remain intact, allowing users and applications access to their files. Not all the file virtualization systems work with DFS or automounters, and some that do don't necessarily require them.

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There are two types of file virtualization products: shared path and split path.

Shared-path file virtualization systems share the control and data path, which means that all connections to the NAS and all data to/from the NAS flow through the virtualization system. Shared-path file virtualization systems are full proxies that touch every file and every packet in the path before it's written or read.


  • Allows files to be migrated in real-time even when in use; the file virtualization system updates the global namespace with the new physical location of the file
  • Intuitive
  • Easy to operate
  • Protects current investment
  • Transparent retirement of older NAS or file systems
  • Individual file-level granularity
  • Heterogeneous NAS and/or file server support; eliminates NAS system lock-in
  • Definable policies using file metadata such as file type, creation date or when last accessed


  • Added latency to pass through file virtualization system can be a bottleneck affecting response times and IOPS
  • Single point of failure; a dead-box failure cuts off all access to the NAS and/or file systems
  • Scalability is limited by the throughput of the shared-path file virtualization system

This was first published in February 2010

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