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How to choose an architecture for branch office storage

In its own way, branch office storage architecture is nearly as complex as choosing a storage architecture for an enterprise data center.

While the implementation of branch office storage is much less complicated than a data center's, you still need to consider many factors to determine a cost-effective architecture that will meet your office's current storage needs and in the future.

You first need to look at each of the three different models for a branch office.

Decentralized model
The most decentralized model uses storage directly attached to individual servers (DAS). The centralized model combines all storage resources into a central pool, either locally or at a remote data center. The hybrid model uses a mix of storage types, including DAS, NAS (network-attached storage) and possibly a SAN (storage area network) to store data.

The decentralized model is probably the most common for branch offices since it is the simplest and cheapest to implement and puts the fewest demands on support personnel. It is also the hardest to manage, the most inefficient in using available storage space and requires provisions for backup, such as backup over the LAN.

Centralized model
The centralized model with storage located at a remote data center has several advantages. It's the easiest to manage, makes the best use of storage capacity, gives the best backup options and is the easiest to upgrade. However, remote centralized storage depends critically

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on the reliability and speed of the WAN connection, and it is almost always slower than local storage.

A centralized model with the storage at the local site, such as a SAN, offers high scalability and faster data access while still giving good manageability. However, it is often the most expensive of the approaches because of the need to establish a separate, fairly sophisticated storage facility in the branch office. It can also pose support problems because of a lack of technically knowledgeable personnel on site. Often, companies choose this model when the branch office is likely to expand significantly in the near future.

Hybrid model
The hybrid approach combines decentralized storage with some additional local storage resources serving the entire site. For example, much of the data may be kept directly attached to the workstations or servers, but an additional layer of storage will be provided by NAS filers connected to the network. Devices attached to the network, then, would handle backup.

The hybrid model is in some ways the most difficult to design because, to get the maximum benefit, it needs to be carefully matched to the present and future needs of the local office. For example, in a hybrid storage architecture, deciding what kinds of data will be kept locally and what will be kept centrally is very important. Properly done, the hybrid model provides a good mix of scalability, data access and ease of support.

One complicating factor in designing storage for a branch model is the potential support cost of getting it wrong. By their nature, branch offices don't have the kind of resources for troubleshooting and support that a data center does, which means additional support, especially on-site support, can be disproportionately expensive.

Microsoft discusses branch office storage architecture in its TechNet paper on reference blueprints at: http://www.microsoft.com/technet/itsolutions/wssra/raguide/ArchitectureBlueprints/rbabst_1.mspx.


Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.
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This was first published in October 2005

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