Why NAS virtualization?

As with SANs, NAS virtualization promises easier storage management and lower storage management costs.


Storage virtualization, in general, has become a requirement for many high-growth enterprises. Why? Because without it, users will continue to manage storage elements as discrete resources, which is fine when you have a few but impossible with many. Virtualization products, regardless of application, are designed to allow users to manage more storage assets with fewer people and to deal with the tsunami of online growth without drowning. By virtualizing storage, users finally are able to create a manageable environment out of chaos.

In the storage area network (SAN) space, SAN appliances virtualize "block" data devices such as disk arrays. This allows users to have many heterogeneous disk devices in a SAN, seen to the "cloud" as a single group of blocks parsed out securely (hopefully) to whatever servers/hosts need to view each logical device. Network-attached storage (NAS) virtualization works under the same principle: Multiple physical NAS systems are "aggregated" and can be seen and managed as a single NFS/CIFS instance.

Who's doing what

NAS market leaders Network Appli-ance and EMC currently do not provide virtualization, as we've described it, although they are expected to in the future.

Tricord builds a NAS "system" in which many boxes equal one logical box, and users can scale bandwidth, IOPS, and capacity by adding incremental boxes. Tricord's Illumina aggregation software re-maps data from physical to logical addresses and re-allocates data across multiple devices. This ap-proach uses a distributed cluster-like file system that maintains overall control of the logical system. (For more information on Tricord's approach, see Info-Stor, January 2001, p. 1.) Viathan, a software start-up based in Seattle, is building a file virtualization engine that will let users of multiple NAS boxes-regardless of the manufacturer-be viewed and managed as a single virtual instance. In theory, they will be able to make data-movement decisions based on policies.

Illumina software allows users to aggregate multiple Lunar Flare NAS appliances into a single, shared cluster, which is managed as a single entity.
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There are many other start-ups expected to jump into NAS virtualization over the next year. Several Israeli companies, including Exanet and Cloverleaf, along with U.S. start-ups such as Pirus, LeftHand Networks, CategoryWare, Broadband Storage, 3ParData, Yotta Yotta, and Cereva Networks will have plays in this space. You can also expect Veritas Software to have a strong play in this market. Virtualization is "hot" because it is necessary, and we'll see a lot of action over the next year.

Steve Duplessie is a senior analyst with Enterprise Storage Group (www.enterprisestoragegroup.com) in Milford, MA.


There is already considerable confusion around what means what, so here is some suggested nomenclature:

NAS-transfers data at the file level.
SAN-transfers data at the block level.
Block virtualization-the ability to create a single unified pool of block storage assets out of many disparate physical devices.
SAN appliance-provides block virtualization across multiple physical arrays but will also offer storage-centric applications such as remote mirroring and serverless backup etc. (see "Business benefits of server-free backup," on p. 40).
File virtualization (NAS)-the ability to create a single unified exported file system (e.g., share) out of multiple heterogeneous standalone NAS systems.
NAS aggregation-similar to "file virtualization" but assumes a single-vendor solution that encompasses multiple (therefore scalable) physical elements into a single logical solution.

This article was originally published on April 01, 2001