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NAS heads: Gatekeepers for enterprise storage

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Global namespace option

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Not every organization has the flexibility to centralize all of its NAS head filers in one location, but many still want to give users the ability to locate and access data regardless of where it resides. Global namespace technology provides this capability. Products such as Acopia Networks' ARX6000 switch virtualizes files by gathering the meta data from the files located on different NAS heads.

The ARX6000 catalogs these files and re-presents the meta data as a common, central file system to users. When users or servers request a specific file, rather then searching the network for the correct NAS head, their file requests go to the ARX6000 which redirects requests to the appropriate NAS head. Similarly, when new files are created and saved, the ARX6000 redirects save requests to the appropriate location on a NAS head and catalogs the file names and locations for future reference.

Despite its benefits, storage administrators need to deploy this technology judiciously. For instance, users may bypass the global namespace server and create, update or delete a file on a specific NAS head. How global name servers handle and adapt to those potential pitfalls will ultimately determine the long-term adoption of this technology.
Advanced features
Advanced back-end storage features like dynamic storage allocation, volume and file system extension, and data re-striping abilities were previously found only on NAS heads supporting same vendor solutions, but they're starting to appear in heterogeneous environments. Examples include BlueArc's and NetApp's NAS heads, which give users the ability to implement these features in heterogeneous storage environments.

BlueArc's Titan SiliconServer allows users to run what-if scenarios based on policies they define. If a storage administrator likes the results, the policy can be implemented to move data across various tiers of storage. NetApp uses its SnapMirror and SnapVault applications in conjunction with products from other vendors for data movement. However, these features don't negate the need for array-specific products like Symmetrix Optimizer for EMC Symmetrix arrays or HiCommand for Hitachi Data Systems arrays that identify hot spots internally within these arrays and optimize their performance.

Thin provisioning, which gives administrators the ability to grow or shrink file systems or volumes dynamically, can help to manage files that have been centrally located on a NAS head. With the 7G release of its Data Ontap operating system, NetApp provides the ability to either expand or shrink volumes on the fly. Its FlexVol technology further complements this capability in heterogeneous storage environments by aggregating pools of disk and then striping the data across these pools, increasing read and write performance.

Cisco Systems Inc.'s recent announcement that it will resell and support EMC's Celerra NAS services enables organizations to present their users with a single point of access to files across the enterprise using their existing Cisco network infrastructure. Marc Staimer, president of Dragon Slayer Consulting, Beaverton, OR, considers the new alliance a big win for Cisco, EMC and users. It gives Cisco a complete end-to-end solution, allowing them to offer WAFS and NAS through a single interface, and EMC gets a new channel for its NAS products similar to its deal with Dell to sell Clariion CX arrays. Most importantly, the partnership provides users with a complete end-to-end storage solution.

Global namespace
As organizations look to consolidate and centralize their NAS infrastructures, the ability for NAS heads to support a global namespace becomes more important. A global namespace partially solves the problem of each NAS head--whether it has direct- or network-attached storage--being a storage island that's unaware of the files stored on other NAS heads. A global namespace running on an existing NAS head or as a dedicated appliance gathers file system meta data from all the NAS heads it can detect, catalogs it and presents this data as a virtual interface to servers requesting files. The appliance or NAS head supporting global namespace becomes the central interface for servers requesting files, redirecting requests to the specific NAS heads hosting the requested files.

NetApp offers global namespace functionality as part of its Virtual File Manager software; EMC plans to support this functionality leveraging Microsoft's DFS and NFS 4.0. For now, EMC works with companies like NuView to provide a global namespace for its environment.

Features like global namespace, heterogeneous storage, policy management and thin provisioning that are available with some NAS head offerings give users the ability to move from an ad hoc NAS environment to a more disciplined management approach. With NAS heads now large enough to support nearly any configuration and protocols like NFS, CIFS and iSCSI, NAS/SAN convergence is becoming a reality.

This was first published in March 2005

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