Direct-attached storage still performs a pivotal role for supporting database servers and other intensive storage applications. But a growing number of enterprises are steering storage away from servers and toward high-speed external fabric.
PJM Interconnections LLC bills itself as the "Nasdaq for energy trading," serving the competitive wholesale electricity market in Pennsylvania, Maryland and New Jersey. Data on energy transactions constantly flows to the Norristown, Penn.-based company's 18 IBM enterprise storage servers. To keep pace with its increasing data load, networked storage was the only logical choice, according to Rich Brenton, PJM's senior technical adviser.
PJM wanted to reduce the cost of adding storage capacity while still providing flexibility for future growth. So the IBM shop attached IBM's Ethernet/IP product, known as NAS 300g, to its 10-terabyte storage area network (SAN). Users see the 300G as a network attached storage (NAS) device, able to serve multi-protocol files and enable access to storage on the SAN. "By centralizing data storage we get a better view of planning and backup scheduling. Dynamic allocation of storage space allows us to make more efficient use of our capacity," said Brenton.
PJM epitomizes the trend to decouple storage from computing power. More and more companies are moving storage away from internal machines to external, high-speed fiber. Of nearly 300 enterprises surveyed, Gartner Group of Stamford,
DAS -- the traditional mode of storage for many enterprises -- is still popular with database administrators due to its ability to quickly replicate high-availability applications. However, DAS systems have limited scalability. New drivers must be added to increase storage capacity, which in turn causes network downtime. The more components you add, the greater your chances of failure or malfunction.
Whereas DAS connects to a single local server on a network, networked storage presents storage as a transparent pool rather than a single machine, available to all users simultaneously. Each server in a networked environment is able to communicate and share data with other machines. There are two main types of networked storage systems: network attached storage (NAS) and storage area networks (SAN). NAS devices connect to a network, rather than specific individual machines, using Ethernet. Network-attached storage operates across multiple platforms, and provides access to storage devices equally from servers and workstations.
Storage area networks can provide even higher throughput and greater scalability than network-attached storage. A SAN sends data over high-speed fiber connections, using routers and switches. Since it only carries input/output traffic, and not other applications, user bottlenecks are reduced. Also, the shared storage feature of SANs enables enterprises to centralize information management and make better use of storage resources, be they on tape or disk.
Another trend also is emerging, analysts say: the convergence of SAN and NAS storage technologies to provide virtual pools of storage. In a converged environment, multiple servers with different interfaces attach to the same storage pool, with each machine able to communicate with the other devices. "Convergence enables companies to provide file-level sharing and backend storage. It helps you better manage storage assets, rationalize your storage infrastructure and utilize all throughput," said Stan Zaffos, an analyst with the Gartner Group.
It had been thought by some experts that NAS and SAN would emerge as competing systems. Instead, they are more likely to be used in tandem, said Randy Kerns, partner with research firm The Evaluator Group in Denver, Colo. "Five years ago there was virtually no consolidation. Three years from now consolidation will be dominant," said Kerns.
Companies are migrating to networked storage because it offers performance and manageability advantages, according to Christopher Poelker, a storage architect with Hitachi Data Systems. "A lot of companies add servers to grow storage, but the cost of adding new servers is getting pretty out of hand," said Poelker. "Companies wind up paying for computing power they don't really need."
Since access to real-time data is the lifeblood of many enterprises, network downtime has to be reduced, if not eliminated. DAS topology requires IT administrators to take systems down for backing up and restoring data, adding new servers or performing other network maintenance. Networked storage architecture, especially SANs, permit backup and restore to occur over Internet protocol using high-speed bandwidth, so data is available without interruption to users. SANs also are equipped to handle large blocks of transactional data.
"Most clients support a heterogeneous environment, usually with one to three Unix elements, Windows, frequently Netware, maybe even a mainframe or Unix. It's a fairly complex environment, so provisioning is a major undertaking," said Zaffos of Gartner. Dynamically allocating storage, as it is needed helps boost utilization rates, a key driver in lowering total cost of ownership. Most Windows environments are using between 20% and 30% of their installed storage capacity, according to Zaffos. Companies running Unix are slightly higher, between 30% and 40%.
Separating storage from servers has some obvious benefits, but Brenton notes there is a steep learning curve. Your IT staff will have to quickly come up to speed on installing Fibre Channel switches, configuring LUN interfaces and anticipating data traffic routing -- all absent in DAS environments. Aside from the technical glitches, companies also need to do a thorough cost-benefit assessment. Installing SAN technology isn't necessarily cheap. PJM looked at estimated costs over a three-year period to determine its return on investment. According to Brenton, his company extrapolates a savings of several thousands of dollars in administrative costs alone each year. "You have to look at the features that you wouldn't get by not having local storage, plus the performance gains," said Brenton.
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This was first published in June 2002