Suppliers of storage systems are starting to move beyond their old debate over the merits of two technologies — storage area networks and networked-attached storage — and are embracing both.
SANs and NAS have distinct profiles and different environments in which they work best. But most experts agree that both will play a role in corporate networks far into the future.
Now, a new round of start-ups is trying to combine the advantages of each. Companies such as DataCore Software, Nishan Systems, Pirus Networks and Vicom Systems offer ways to take advantage of the best aspects of SANs and NAS by producing software and devices that work with both.
"The SANs-vs.-NAS talk started heating up a year ago. We think its more about SANs and NAS," says Michael Smith, executive vice president of marketing at Emulex, a supplier of Fibre Channel host bus adapters for SANs.
A SAN provides a dedicated — though comparatively expensive — high-speed subnetwork for moving data. NAS, on the other hand, uses the existing network infrastructure to exchange data among applications. But increasingly, the two approaches to storage dont need to be mutually exclusive, technology suppliers say.
"Were not setting up barriers — were taking them down," says Tom Clark, director of technology marketing at Nishan, a producer of SAN switches and routers that communicate with Internet Protocol (IP) networking devices.
That sentiment is shared by other vendors that offer ways to make storage systems play well together. "We dont care about the plumbing. We dont care whether its SAN or NAS," says Augie Gonzalez, director of product marketing at DataCore, maker of SANsymphony, a cross-platform storage management system.
Both approaches will be required as the need for storage capacity doubles every 13 months, says Randal Sagrillo, director of marketing for network storage at Sun Microsystems. Sales of SAN and NAS systems are expanding at close to 100 percent per year for most vendors, according to Sun. "The network — including the Internet — explodes the amount of data moving around the world," Sagrillo says.
And in the fast-changing storage world, SAN and NAS technologies are evolving at a rapid clip.
Storage — disk drives, or combinations of drives known as arrays — used to be directly attached to the server with which it worked. Data was driven over a cable between the two, typically using the Small Computer System Interface, powered by a SCSI interface card in the server and SCSI controllers on the storage disks. This form of storage remains in place, but is not growing, industry experts say.
Then came NAS, which evolved as a more flexible way of configuring a set of disks that could work with many servers in different locations. A common form of NAS is the "thin server" used as a storage appliance. Thin server vendors include Network Appliance, Sun and VA Linux Systems. The server is loaded with disk drives, plugged into a rack and connected to the network through an Ethernet network interface card.
SANs emerged as a third option with the maturing of fiber-optic devices and a networking technology called Fibre Channel, designed for fast, efficient storage. A SAN is built out as a separate storage subnetwork, usually in the data center, to optimize storage data flow. Fibre Channel-based SANs now have a strong group of backers, including Agilent Technologies, Brocade Communications Systems, EMC and Emulex.
Today, many enterprises are installing Gigabit Ethernet, which transmits data at up to — theoretically — 1 gigabit per second, as the foundation for their network backbones. Adding NAS to such high-speed Ethernet networks opens up new efficiencies for NAS, which is generally viewed as slower than SANs.
SANs, meanwhile, are about to increase their throughput capacity from 1 Gbps to 2 Gbps, again outstripping Ethernet, says Sam Tam, CEO of Vicom, a supplier of storage virtualization software for pooling SAN and NAS resources. "NAS tends to be lower throughput, but more mature. SAN offers better throughput, but its more complicated," Tam says. Consequently, SANs frequently occupy the data center, where their speed moves data from databases and file systems to many servers.
A SAN offers better throughput because its a specialized subnetwork optimized for storage. By dealing with data in blocks, it can extract large amounts from a database and move that data to the server quickly. A Fibre Channel frame holds 2,112 bytes, while an Ethernet packet is 1,500 bytes. Also, Fibre Channel provides a stripped-down networking protocol, whereas IP running on Ethernet in a NAS environment is a processing-intensive, general-purpose protocol, says Spencer Sells, product marketing manager at Gadzoox Networks, a SAN equipment vendor.
But NAS has a few key advantages over its faster cousin. The setup time for a NAS appliance is minimal, particularly if youre simply sliding a thin server into an equipment rack. And the skills needed to run the appliance are probably already found in-house.
Also, unlike SAN systems, a NAS appliance is equipped with a file management system that can translate responses to Windows NT and 2000, and Unix or Linux servers — making it a natural file-sharing intermediary between the systems.
"If you need file sharing, as in a workgroup or [for] hosting content, then NAS is typically called for," Emulexs Smith says. "If you want fast, block-level transfers — as in transaction processing — then a SAN is called for."
In a few years, however, hybrid SAN-NAS technologies could make the distinctions obsolete. New standards being developed for both types of networked storage blur the lines between SANs and NAS. The SCSI-over-IP protocol, called iSCSI, is a new Internet Engineering Task Force specification that will let storage systems send SCSI-style blocks of data — the data transfer method used by SANs — over an IP network.
A technology such as iSCSI that allows file-oriented IP networks to accommodate a SCSI-block data handling system has many advantages for storage. For example, an enterprise could move data in efficient blocks from their databases, across their internal networks built on Transport Control Protocol/IP — the protocols of the Internet.
The IETF is also drafting a standard that will encapsulate Fibre Channel communications into IP packets. Called Fibre Channel-over-IP, it would allow an enterprise to connect a SAN at one location with a SAN at another over an IP network — a lower-cost alternative to leasing private data communication lines, says Mark Lovington, vice president of marketing at Pirus. Nishan, Pirus and other companies have implemented early versions of these standards to get to market early with products that bridge the SANs-to-NAS divide.
In the near term, of course, SANs and NAS will remain better suited for different types of applications. But will one win over the other? "I dont think so," says Chris Baldwin, partner at venture capital firm Charles River Ventures, which has invested in several storage companies. "I think its going to be a very heterogeneous world."