Get control of NAS systems


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3. Clustered NAS systems

Clustered NAS systems use a distributed file system running concurrently on multiple NAS nodes. Data and metadata can be striped across both the cluster and underpinning block (direct-attached storage [DAS] or SAN) storage subsystems. Clustering also provides access to all files from any of the clustered nodes regardless of the physical location of the file. The number and location of the nodes are transparent to the users and applications accessing them.

Although clustering appears similar to file virtualization, the key difference is that all system nodes must be from the same vendor and often configured similarly. Some exceptions to this include BlueArc Corp.'s Titan and Mercury series, and NetApp's Ontap GX.

Clustered NAS systems typically provide transparent replication and fault tolerance, so that if one or more nodes fail, the system continues functioning without any data loss. Clustered NAS systems are distinguished by their large file systems that can scale to hundreds of terabytes (or more) of addressable capacity.

Clustered NAS systems include BlueArc's Titan and Mercury series, EMC's Celerra NS-960 with Multi-Path File System (MPFS), Exanet Inc.'s ExaStore, Hewlett-Packard (HP) Co.'s Ibrix Fusion and StorageWorks Scalable NAS (previously known as PolyServe),

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Hitachi Data Systems' HNAS and 3200 series, IBM Corp.'s Scale-out File Services (SoFS), Isilon Systems Inc.'s IQ, NetApp's Ontap GX, Panasas Inc.'s ActiveStor and Scale Computing's SN Series.


  • Linearly scale to many nodes and high capacities, with millions to billions of managed file objects; aggregate throughput and IOPS independent of one another
  • Easy to grow
  • Pay-as-you-go architecture
  • Built-in fault tolerance
  • Centralized management
  • Easy data protection
  • Simple file access


  • Rip-and-replace solution; can't reuse current NAS systems
  • No support for heterogeneous NAS systems
  • No ability to migrate files from current NAS systems to the clustered
  • Higher hardware and license costs, but may be offset by significantly lower management costs

Clustered NAS does a very good job of resolving most network-attached storage sprawl challenges. It eliminates or at least mitigates the multisystem management issue depending on the scale of the environment. User and application access is simplified with load balancing built in, and data protection and replication is also part of the architecture. Clustered NAS does fall a little short on storage tiering; it does make it easier, but doesn't automate the process (with the exception of EMC's Celerra NS-960 with FAST using Rainfinity).

This was first published in February 2010

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