NAS and SAN are complementary

NAS and SAN are complementary

Network-attached storage can be used as a stepping stone to storage area networks, or it can coexist with them.

Bob Williamsen

Traditional server-attached storage is not equipped to handle companies` growing data storage and access requirements. Neither are traditional storage architectures, which lack the scalability, reliability, bandwidth, latency, and manageability to cost-effectively meet increasing demands. The answer: shared networked storage in the form of network-attached storage (NAS) or storage area networks (SANs). The two approaches are often described too simply or too complexly, and they are often portrayed as competing, rather than complementary, technologies. Perpetuating the confusion is the storage landscape, which is littered with proprietary solutions.

Regardless, the most effective data storage solution is the one that best meets your company`s needs and provides the best return on investment. Because storage technology is changing so rapidly, it is important to invest in hardware and software that grows with your company.

As the market for NAS and SAN expands, storage vendors are providing products that meet a wide spectrum of user needs--from workgroup and departmental devices to enterprise systems. Some are offering flexible architectures and products that can be configured in a NAS, SAN, or mixed environment, while others are fixed-function devices with varying levels of compatibility between NAS and SAN. The ability to reposition, rather than replace, storage hardware and software has the immediate benefit of lowering total cost of ownership while providing continuity for existing users.

To understand how to deploy NAS and SAN, first you need to understand the unique benefits of each. NAS provides a storage front-end that facilitates cross-platform file sharing. SAN allows for storage hardware, network resources and raw data sharing, supporting back-end departmental and enterprise storage.

Network-attached storage

NAS systems--that is, any storage device that is directly attached to a LAN--were developed to meet users` needs for a less-expensive and less time-consuming way of consolidating storage and cross-platform file sharing on heterogeneous networks. They have only one purpose: serving files to network users.

NAS servers enhance network performance by eliminating server I/O bottlenecks. LAN clients access these devices over standard network protocols such as TCP/IP and can share files simultaneously across different protocols such as CIFS, NFS and HTTP, which means they are server- and operating-system independent. This makes it easy for system administrators to add, maintain, and access large amounts of storage capacity.

NAS systems are not limited to read/write disk systems, but also include optical media systems such as CD-ROM and DVD-ROM servers. In addition to basic file service, NAS can be used for specialized tasks such as e-commerce, Web caching, local storage, remote storage or caching in a hierarchical storage management (HSM) environment. Because NAS servers are designed from the ground up as storage devices, they are engineered for high performance.

A basic disk-based read/write NAS system includes an enclosure, power supplies, cooling fans, network connection(s), hard disk drives, a backup device and a scalable controller. NAS systems can be designed around nearly any operating system, from embedded real-time operating systems to Linux or compact operating system kernels optimized for file serving. Tasks include managing the network connections, accepting file requests, sending and receiving data from the disk drives, returning data to the clients, and monitoring the overall health of the system. Benefits include:

•Ease of use. NAS brings ease of use to shared networked storage. NAS devices are as easy to add to a LAN as a PC or a printer. And storage can be added as needed without disrupting the network--eliminating the downtime associated with server-attached storage.

Best of all, NAS devices are plug-and-play "appliances." Setup requires little more than connecting to the network, applying power, and performing a few mouse clicks. Because NAS configurations provide fully integrated hardware and software, they are much less complex to deploy than typical general-purpose network servers.

•Performance. NAS systems off-load data from the network backbone by providing storage to a workgroup or a department on an independent--but connected--subnet, or network division. Unlike server-attached storage, NAS separates file-serving services from application processing. NAS servers are not burdened by application function overhead, which improves the overall effectiveness of both the NAS and the LAN. The application server is not only faster, but the likelihood of a system crash is also less. Administrators can also use NAS-integrated tape devices to automate backup functions and eliminate LAN backup traffic.

Departmental/workgroup NAS systems often meet the following criteria:

•SAN-enabled. The back-end of the NAS box includes a Fibre Channel port that can be connected to a SAN. This enables the NAS, via shared storage resources, to take advantage of all of the SAN capabilities, including centralized off-LAN backup and capacity expansion.

•A comprehensive storage management framework. A storage management standard has not been established for NAS appliances. Administrators should seek companies with a NAS and a SAN management strategy in order to leverage NAS investments into the future.

•LAN-free backup. Departmental systems must backup and protect critical data. LAN-free backup allows the system to back up user data onto a local device without using precious LAN bandwidth, protecting users` data while enabling higher LAN performance.

Storage area networks

Although some vendors offer proprietary SANs, most storage experts define a SAN as an open Fibre Channel architecture for interconnecting storage systems, backup devices and servers. SANs often employ a network topology referred to as a fabric. The strength of switched Fibre Channel fabrics lies in gigabit-per-second data transfer, compatible hubs and switches that channel data traffic between servers running heterogeneous operating systems and the ability to handle multiple arrays of tape libraries that archive and process data and perform enterprise backup off the client network.

Conceptually, a SAN is a dedicated storage network in which systems and intelligent subsystems (primary and secondary) communicate with each other to control and manage the movement and storage of data from a central point. SANs allow for nearly unlimited storage configurations, where any server or storage system can exchange data with any other server or storage system.

SANs combine high-performance Fibre Channel I/O with network connectivity. By attaching devices to a network, SANs address the problems of scalability, management, capacity and bandwidth. Diverting most of the data traffic off the LAN and onto the SAN removes the data glut from the LAN. This greatly increases network performance and client productivity while freeing up bandwidth for timely, efficient backups.

The key to a successful SAN--particularly in the enterprise space--is intuitive, easy-to-use management software that links the storage network to other enterprise management tools. Initial SAN implementations have been limited to simple point solutions that do not require a high degree of management support. Such implementations, however, are difficult to install, lack comprehensive storage management software, and have been plagued by interoperability issues. When comprehensive management software becomes available, SANs will become the obvious next step for workgroup, departmental and enterprise storage systems.

The foundation of a SAN is the hardware on which it is built (e.g., Fibre Channel host adapters, hubs, switches, bridges/routers/ gateways and Fibre Channel-attached storage devices). But to provide basic services to SAN devices, a system also needs device discovery, topology mapping, storage access/permission mapping, and event notification features.

SANs will enable seamless centralized administration, backup, resource sharing, HSM and policy management of multiple hardware and software technologies. SANs will also provide storage services to the most advanced data centers requiring data sharing, complete fault tolerance across heterogeneous environments, full WAN connectivity and increased performance.

How to extend from NAS to SAN

A SAN`s data routing capability allows it to connect to existing NAS systems and LANs either by bridges or by NAS systems designed to work in a SAN. This means that a company`s investment in NAS can be completely leveraged into the future.

SANs can convert data traffic from one protocol to another and provide connectivity to other network protocols such as ATM and Ethernet. By adding WAN connectivity, a SAN system can offer worldwide mirroring or data replication to provide a corporation with complete disaster recovery.

NAS can act as the front end for many SAN functions. A SAN can be used as a type of storage module for NAS in a modular system setup. A SAN can also provide the backup portion of the NAS.

Let`s look at a typical NAS/SAN migration. An IT department purchases a NAS system to consolidate storage for multiple NT and Unix file servers. The NAS system includes:

•A controller with one gigabit Ethernet port and one Fibre Channel Arbitrated Loop (FC-AL) port

•Two Fibre Channel disk systems

•One tape library

The administrator installs it as a standalone system, but only at 25% capacity due to restructuring and internal issues.

The IT department now installs a SAN to consolidate storage and improve backup performance for its database servers. The administrator also wants to remotely mirror a critical portion of the NAS data. IT simply connects the NAS controller, the two Fibre Channel disk systems and the tape library to the SAN via a Fibre Channel switch. The administrator uses storage management software to assign 50% of the drives to the NAS controller and 50% of the drives to the database servers, saving significant money by reallocating existing hard drive resources previously dedicated to the NAS system.

When the NAS system requires more storage to meet the increasing storage needs of users, the administrator can allocate it from other free resources on the SAN. All servers can share the tape library. Finally, the administrator repositions NAS data onto an existing SAN disk array that provides remote mirroring. This saves additional costs because the SAN eliminates the need to purchase an additional mirroring system.

NAS and SANs are complementary, not competing, technologies. NAS can act as a standalone system, or as part of a SAN. In migration scenarios, NAS is a stepping stone. In other scenarios, it is the best tool for the job. It would be a strategic mistake to view these networking architectures as an either/or proposition. When it comes to departmental, workgroup and enterprise storage, NAS and SAN both have a place.

Click here to enlarge image

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Bob Williamsen is the vice president of marketing at Connex (www.connex), a Western Digital company, and can be reached at sknodl@connex.com. Connex is located in San Jose.

This article was originally published on September 01, 1999