Storage

Storage-area networks: The smart person's guide

​This primer on storage-area networks covers what small, medium, and large businesses need to know about this method of storing large quantities of primary data.

Image: iStock/Vladimir_Timofeev

Storage-area networks (SANs) established their role as the heart of enterprise-level primary storage in the early 2000s. At first, SANs were expensive and proprietary, but since the 2010s, SANs have become more affordable and standardized — there are even open-source options. This guide is an entry-level primer on SAN technology.

Executive summary

  • What is it? SANs are a high-performance method of storing large quantities of primary data.
  • Why does it matter? Traditional direct-attached server storage is limited in capacity and accessibility. Using a SAN solves both issues and maintains read/write speed. It is also helpful for disaster planning because data can reside separate from servers.
  • Who does this affect? SANs are typically purchased by medium-to-large organizations, or by small organizations with large data requirements such as civil engineering, defense, and pharmaceutical firms.
  • When is this happening? Yesterday, today, and tomorrow. SANs are approaching 20-years-old; however, there are always fresh companies and perspective in the storage industry that seek to give SANs new life.
  • How do I get it? Initially just for large enterprises, SANs are now available to the mass market. Mid-range versions are sold by resellers and directly from storage companies. Open-source software is available to build your own SAN.

What is a SAN?

SANs are a method of connecting large quantities of hard drives in an array and presenting them as a vast repository of block-level data to computers on a network. SANs differ from network-attached storage (NAS), which are similar products that also gather large quantities of drives into one, but present it directly to a network like any other file-based server.

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Why do SANs matter?

The main reason to use a SAN is to keep terabytes or petabytes of data at-the-ready for use with time-sensitive applications, especially those residing atop relational databases. End users should still keep personal files on their local drive, department file servers (which could be NAS), or on a private cloud, while backup storage usually targets conventional tape libraries.

SANs can use many types of hard drives. Enterprise-grade products, which combine SCSI drives mated to fiber channel (fiber optic) interfaces, can spin around 15,000rpm, and are priced high to match their performance. IP-based systems such as iSCSI have pros and cons, such as simpler infrastructure but with slower connections. Serial ATA drives are cheapest and slowest.

Another major benefit of using a SAN is disaster recovery. By placing the SAN separate from servers, data can be preserved if there is physical damage to a data center. Storage networking vendors make a variety of long-distance data replication technologies for further peace-of-mind. As with the drives, such technologies can work over dedicated storage switches or more common Ethernet routers.

Maintenance is also a big factor. Software virtualization software allows administrators to assign logical drives whenever and wherever they're needed, without concern to the physical level. You can create multiple virtual SANs inside one physical system. Most impressive of all, you can virtualize storage components from different manufacturers, which was impossible when SANs debuted.

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Who does this affect?

Large and midsize enterprises almost certainly already own one or more SANs or are at least considering their options. Like any high technology, SANs are gradually becoming more available to ordinary businesses.

Cloud storage or large-scale NAS may keep SAN technology from reaching smaller organizations, though open-source SAN software running atop what's known among insiders as JBOD ("just a bunch of disks") is starting to gain credibility; therefore, the future of SANs in small organizations remains open for debate. A likely future may see the open-source approach take hold only in technical organizations. Larger organizations are already starting to move on to the next big thing — SANs filled with flash memory instead of traditional hard disks.

Once a company decides to shop for or purchase a SAN, this impacts everyone from executives to end users. Managers may wish to consider modifying workflows to take advantage of improvements in data performance and reliability; finance departments need to consider the costs; IT leaders will need special training or the budget to hire a storage administrator; and end users may need to learn different storage practices.

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When is this happening?

This is happening right now. SANs are not an emerging new category — they're here today, and larger organizations spend millions of dollars on SAN technology every year.

SANs are evolving. Their network aspects are becoming more mainstream, while the actual storage inside a SAN is becoming more exotic. SANs used to be all about special hardware, but now they're more about rather ordinary chassis using special software (such changes, along with down-market availability, are why we felt this guide to be necessary).

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How do I get it?

The answer is, "It depends." If you're with a large organization, then contact any of the major players such as EMC (soon to be Dell), IBM, Hitachi, or HP Enterprise. You may be referred to a local reseller.

There are many second-tier suppliers who are more willing to sell directly to smaller companies. Consider hiring consultants who can guide you through the SAN purchase, installation, and maintenance process.

Remember: A SAN is an extremely powerful tool, though it's not for the faint-of-heart.

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About

Evan Koblentz began covering enterprise IT during the dot-com boom times of the late 1990s. He recently published a book, "Abacus to smartphone: The evolution of mobile and portable computers".

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