Networking's greatest debates in the Data Center

NAS vs. SAN

The argument over the humble file serving network-attached storage and the data-intensive storage-area network is a popular topic for the less than storage-savvy industry pundit. But a battle between NAS and SAN was never meant to be. NAS came out of the NetWare and Microsoft file servers used in the 1980s to provide access to files for network clients. Network Appliance first commercialized the concept of a NAS appliance, which would serve up files and be based on a stripped down network operating system.

NAS has been adopted by legions of Network Appliance users and bunches of Windows users for hosting Microsoft Exchange and SQL Server. It is used by millions of others for storing their file-oriented data.

SANs were adopted to partition storage traffic from the rest of the LAN and by doing so, speed up transaction-intensive databases, ERP and CRM systems.

"Separating ownership of a server from its storage and placing all the storage devices directly on a Fibre Channel network allows a many-to-many connection from servers to storage, and from storage to other storage devices. This approach grants the benefits of traditional networking to storage devices, such as increased scalability, availability and performance," consultant Barb Goldworm once wrote in a Network World newsletter.

SAN backers say the technology is best when performance is paramount for business-critical applications such as databases, ERP or CRM systems. NAS, they say is hindered by performance concerns. If you talk to some of these NAS users though, they will say that using NAS to host business-critical applications has never been a problem.

A recent test of a BlueArc NAS system showed more than 192,900 operations per second. -Deni Connor

Fibre Channel vs. iSCSI

Fibre Channel is dead." That was the controversial conclusion of one participant in a heated debate at an industry conference in 2000. Industry vendors were investigating a new protocol -- storage over IP -- that they said would replace the then dominant Fibre Channel. That newfangled transport protocol, which allowed storage traffic to flow across the Gigabit Ethernet network, would become iSCSI -- it would be implemented by individuals who were familiar with Ethernet networking, but not with the more complicated and expensive Fibre Channel.

Spin forward seven years and the battle between Fibre Channel and iSCSI is now passe. Fibre Channel isn't dead -- it's still the dominant storage protocol -- and iSCSI is being implemented at an increasing rate. According to IDC, while iSCSI commanded just 3 percent market share in external disk storage systems (with Fibre Channel accounting for the rest), the research firm expects that market share to increase to 21 percent by 2010. Now the two technologies even exist in the same network.

Fibre Channel is being used in enterprises to host transaction- and data-intensive operations because of its performance and its assured delivery of data; iSCSI, an inexpensive technology that operates on top of Gigabit Ethernet, is being used by organizations that don't have dedicated and storage-savvy IT personnel and in small and midsize businesses and departments in the enterprise to host mid-range business-critical applications that do not require the blazing performance of Fibre Channel.

Today, the industry is vetting iSCSI to run on 10Gbps Ethernet, where it can take advantage of TCP offload, remote DMA and I/O virtualization capabilities. Research firm Dell'Oro Group sized the 10Gbps Ethernet switch market at 100,000 port shipments in the fourth quarter of 2006 with revenue of US$1 billion. As 10Gbps Ethernet continues to grow, there may be no way to stop iSCSI's market momentum.

Fibre Channel, on the other hand, may at some time be replaced by the proposed Fibre Channel over Ethernet (FCoE), a technology that relies on the lossless, enhanced Ethernet specification. This technology, which layers Fibre Channel over Ethernet, will be attractive to companies that want to operate storage and networking on a converged network. FCoE products are expected to be available from Cisco, Brocade, Network Appliance, Nuova Systems, Emulex and QLogic sometime in 2009. -Deni Connor