Storage area network fundamentals: The right questions to ask

Will a storage area network be a good fit in your IT environment? Consult our guide to storage area network fundamentals, including how to evaluate your current setup and needs.

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This is the first story in a three-part series about the role of the storage area network (SAN) in midmarket organizations.

Storage area networks -- shared storage solutions accessible by multiple servers -- are growing in popularity among midsized organizations. As businesses grow and change, SANs can help organizations increase technology utilization and alleviate some data storage management complexities. New technologies and vendor offerings have brought SANs within reach for even some of the smallest companies, but it's important to understand whether or not a SAN will be a good fit for your IT environment before you make the investment.

To find out, you need to understand storage area network fundamentals, as far as the right questions to ask, including how to evaluate your current setup and potential requirements, what to look for in a SAN vendor and how to find the right solution to meet your needs.

Understanding storage area network fundamentals

A SAN can mean different things depending on your view or vendor familiarity. In its simplest terms, a SAN is a shared storage solution accessible by multiple servers using some type of interconnect. With a SAN, servers access the shared storage system using host bus adapters, network interface cards/chips or converged network adapters attached to an interconnect (usually a copper or optical cable and sometimes a wireless connection), which is in turn attached to a storage system.

Utilizing a shared storage system prevents some of the bottlenecks that often accompany single-server stored data: pockets or islands of technology resulting in underutilized or wasted resources and/or oversaturated resources unable to support growth. Many SANs also utilize switches between servers and storage devices to increase connectivity flexibility, allowing more servers to attach to a storage system than there are available SAN ports.

Routers and gateways are often used with SANs to facilitate metropolitan area networking and wide area networking (WAN). Using a SAN for centralized data transfer simplifies data protection -- moving or replicating data stored in a common location is more manageable than it would be with sprawled data. This improves business continuity, disaster recovery and high-availability efforts.

Network attached storage (NAS) is a variation of shared data storage, similar to a SAN. But while SAN solutions are typically associated with block or non-file serving storage, NAS solutions provide data-sharing capabilities.

Within a SAN, portions of a storage system are subdivided into Logical Unit Numbers (LUNs) or volumes. It is possible for two or more servers to access and share a LUN with storage sharing software, but it's typically not the case. In most cases, a SAN enables capacity sharing across multiple servers -- subdividing larger storage systems and allocating space for individual servers.

Data sharing, on the other hand, enables multiple servers to share storage capacity and concurrent read-and-write access to a file and its content. For data sharing to occur with integrity and coherency, some form of file-sharing software is required. NAS solutions have built-in shared file systems supporting access protocols, including Unix Network File System and Windows Common Internet File System, in addition to shared storage capabilities.

Understanding the difference between shared block storage and shared data can help you better select the right option for your IT environment. For example, if you're going to be running a couple of servers -- one with Exchange, one with VMware, another with SharePoint and SQL Server and another that is both a Web and file server -- a shared block SAN storage solution may be the best option. This is because some applications and tools only support, or are optimized to work with, block storage. On the other hand, storage for file sharing, home directories and some Web servers might warrant a NAS device. These applications and tools may better leverage the file system inherently built into NAS. There are also multi-protocol solutions providing the best of both worlds, enabling SAN and NAS to meet specific or changing needs.

Determine your SAN needs and requirements

Before you start evaluating the vendor landscape, determine your current and expected storage needs. Understanding your requirements can help you better select a technology offering aligned to your needs. Ask yourself the following questions:

How are you currently storing and using your data?
Do you have a shared storage system across multiple servers? Is the storage built into your servers as dedicated direct-attached storage? How much storage do you currently have? How much free storage do you have? Are there any known performance or response time problems? How are you currently backing up your servers or storage (to tape, to another server or to a deduplication device)?
Why it's important: The answers to these questions will help you understand how you're using and managing your current storage capabilities.

What will you need to support or enable with data storage in the future?
Do you intend to enhance your disaster recovery and business continuity plans? Have you started, or do you plan to virtualize or consolidate servers? How many servers do you expect to have in 12 to 18 months? Will you add new applications to your environment (Microsoft SharePoint, SQL Server, Oracle, video or Web hosting), and if so, are additional resources needed?
Why it's important: The answers to these questions can help you better plan future storage needs based on expected changes in your IT environment.

What are your business requirements?
How fast is your business growing, and how much generated data needs to be stored? Have your data retention needs increased?
Why it's important: If you understand your company's growth rate, you can better size a storage solution to meet your current and future needs.

What is your budget and deployment timeline?
Most of us would like to have a luxury car with all the bells and whistles. While these high-end features are nice, they are usually not requirements. The same thing can hold true from a storage perspective. There are SAN solutions in the high-end Cadillac category -- feature-laden solutions with associated price tags. But there are also value-oriented (not necessarily cheap) solutions providing basic, and sometimes advanced, features to meet various needs.

The bottom line: Find the right storage solution for your IT environment by taking a step backward before going forward and understanding storage area network fundamentals. Determine your storage needs and expectations before you begin to look at your vendor options. In my experience, the No. 1 key to success and customer satisfaction doesn't come from the technology or the vendor as much as from aligning the solution to your business needs.

Greg Schulz is founder of The Server and StorageIO Group, an independent IT industry advisory and consultancy. He has authored the books The Green and Virtual Data Center (CRC) and Resilient Storage Networks. Find him on Twitter @storageio.

This was first published in August 2010

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