Guide to SAN and NAS virtualisation

File virtualisation

Just as block virtualisation simplifies SAN management, file virtualisation eliminates much of the complexity and limitations associated with enterprise NAS systems. We all recognise that the volume of unstructured data is exploding, and that IT has little visibility into or control over that data. File virtualisation offers an answer.

File virtualisation abstracts the underlying specifics of the physical file servers and NAS devices and creates a uniform namespace across those physical devices. A namespace is simply a fancy term referring to the hierarchy of directories and files and their corresponding metadata. Typically with a standard file system such as NTFS, a namespace is associated with a single machine or file system. By bringing multiple file systems and devices under a single namespace, file virtualisation provides a single view of directories and files and gives administrators a single control point for managing that data.

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Many of the benefits will sound familiar. Like storage virtualisation, file virtualisation can enable the nondisruptive movement and migration of file data from one device to another. Storage administrators can perform routine maintenance of NAS devices and retire old equipment without interrupting users and applications.

File virtualisation, when married with clustering technologies, also can dramatically boost scalability and performance. A NAS cluster can provide several orders of magnitude faster throughput (MBps) and IOPS than a single NAS device. HPC (high performance computing) applications, such as seismic processing, video rendering, and scientific research simulations, rely heavily on file virtualisation technologies to deliver scalable data access.

Three architectural approaches

File virtualisation is still in its infancy. As always, different vendors’ approaches are optimally suited for different usage models, and no one size fits all. Broadly speaking, you’ll find three different approaches to file virtualisation in the market today: Platform-integrated namespaces, clustered-storage derived namespaces, and network-resident virtualised namespaces.

Platform-integrated namespaces are extensions of the host file system. They provide a platform-specific means of abstracting file relationships across machines on a specific server platform. These types of namespaces are well suited for multisite collaboration, but they tend to lack rich file controls and of course they are bound to a single file system or OS. Examples include Brocade StorageX, NFS v4, and Microsoft Distributed File System (DFS).

Clustered storage systems combine clustering and advanced file system technology to create a modularly expandable system that can serve ever-increasing volumes of NFS and CIFS requests. A natural outgrowth of these clustered systems is a unified, shared namespace across all elements of the cluster. Clustered storage systems are ideally suited for high performance applications and to consolidate multiple file servers into a single, high-availability system. Vendors here include Exanet, Isilon, Network Appliance (Data ONTAP GX), and HP (PolyServe).