By Hailey Lynne McKeefry
Traditionally, IT shops turned to attached storage methods such as standalone hard disks, RAID arrays, tape media, and optical, which connected a single storage resource to a single host, such as a server or workstation, directly or through an I/O bus. The variety of methods presented an equally wide range of concerns, including cost of ownership, scalability, and manageability issues.
So much for tradition. The storage area network (SAN) and network-attached storage (NAS) have now entered the scene with a bang. These technologies let you share storage resources among a much larger number of processing systems and users for improved efficiency and simplified management. Networked storage technologies also let you access data more quickly, since you can share the data across multiple platforms regardless of the device or operating system you're using.
NAS and SAN defined
Besides the fact that SAN is NAS spelled backward, there's a fundamental difference between the technologies and their mirror-image acronyms.
A NAS is a specific product that sits between an application server and a file system, but SAN refers to the architecture. A SAN is its own network, connecting all storage devices and all servers.
SANs can solve connectivity problems among multiple storage devices and servers. A SAN also offers new approaches to storage, such as disk and tape pooling, heterogeneous data sharing, and off-the-network/serverless backup and restoring. This secondary network relieves the main network of massive data transfer loads because backup traffic occurs only between storage devices inside the SAN.
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A NAS, on the other hand, lets you add storage without taking the network down. And because the NAS is a file-system agnostic, clients can share and access the same information, even if they're using different operating systems. NAS appliances also have the ability to share a data instance on multiple application servers to create cross-platform, collaborative capabilities.
The NAS becomes a separate node on the network in order to let hosts directly access files stored on the NAS. Common applications for NAS include consolidated storage, Internet and e-commerce applications, and digital media. However, a NAS can send files only, not data blocks.
The benefits of NAS and SAN
The two enterprise storage options provide one big boon to the enterprise: drastic IT staffing cost reduction. Storage management consumes about 55 percent of the overall storage budget in a distributed environment. By comparison, SANs bring that figure down to between 15 and 20 percent of the overall budget. And NAS devices are even easier to manage because they simply plug in to the network and are focused on specific file-serving needs. GUI-based management software further eases the administration of these storage systems.
- Easy to add
You can add NAS appliances—which are particularly suited to any application with intense read/write activity—to the network within minutes, without bringing your LAN down.
- Takes the heat off your network server
NAS devices increase storage-on-the-fly capabilities, which you can use to redirect network traffic and reduce the need to add more network nodes. Enterprise managers can offload high-bandwidth file-serving tasks from the network server, reducing latency, which might interfere with critical business tasks such as application handling and e-mail. NAS flexibility lets you add storage wherever you need it, even to remote locations. Finally, with NAS, you can perform backups without affecting network server performance.
- Facilitates data sharing
The modern network is a heterogeneous environment, and NAS lets you connect to multiple operating systems and share data among disparate clients and servers. NAS supports both the Network File System (NFS) protocol for UNIX and the Common Internet File System (CIFS) for Microsoft to facilitate this cross-platform data sharing.
- Consolidates information
The biggest single benefit of a SAN is that it lets you consolidate a huge amount of information into a centralized storage network. The SAN connects all the storage and offloads the network traffic associated with storage access onto the separate network. This translates into lower latency and more efficient resource utilization.
- Faster data retrieval
The fibre channel upon which SAN is based uses an arbitrated loop, which provides true 100-Mbps data speeds. Compare these numbers to today's SCSI technology, which provides mainly speeds of 40 or 80 Mbps, and you have significantly faster data speeds. However, newer SCSI technology is being developed that promises to bring SCSI speeds to near parity. SANs can also support a nearly limitless number of devices if your company is willing to invest in the infrastructure (servers, multiplexers, bridges, and storage devices).
- Easier backup and recovery
SANs make it easier for companies to make backups and effect disaster recovery. Data can be mirrored to a remote location for seamless disaster recovery or backed up quickly to another location without affecting network speeds. With a SAN, you can save gigabytes of data in a matter of hours. In addition, SANs provide a variety of network-enabled techniques—such as alternate pathing, clustering, failover, mirroring, and replication—that protect against data loss and improve the availability of information.
- Exceptional scalability
A SAN, with its inherent and almost unlimited scalability, is a particularly good choice for networks that grow quickly or have sporadic needs for higher storage capacity levels. With repartitioning and management tools, network administrators can reallocate storage space from one server to another simply by repartitioning the SAN. Repartitioning assigns storage space to a network server instead of directly connecting storage space to a network server.
However, SANs do have their limitations. The cost of entry is high, with a medium-size SAN costing as much as $250,000. In addition, a lack of standards presents huge interoperability issues that vendors are just beginning to address.
The buying decision checklist
Security: An appliance that provides good security combines data and network reliability. Look for products that address data security and provide for superior uptime. The Sun StorEdge N8200 NAS, for example, provides the option of adding hot-swap capabilities to ensure the highest level of uptime. The Auspex NS2000 NAS includes NeTservices 2.0 software, which delivers Windows NT 4.0 management tools and security services. If reliability is your key concern, make sure that redundancy features are built in to the hardware you select.
Access time: Particularly in the SAN environment, getting information quickly is critical. NAS devices serve pages and are noted for superior latency levels. SANs serve blocks of information rather than individual pages.
Interoperability: This isn't an issue in the NAS world because NAS devices are simply appliances. But SANs have long been plagued by interoperability issues. Often, vendors recommend buying all parts of the SAN from a single vendor. Others offer extensive interoperability testing and will recommend product combinations that work well together. Dell recently announced its Dell PowerVault SAN Configuration Tool and Dell PowerSuites for Backup and Restore Software to help customers more easily create heterogeneous SANs. IBM has developed its Seascape architecture, which combines snap-in hardware and software building blocks that let customers build solutions optimized for specific business environments. IBM's Seascape building blocks, which include IBM's Versatile Storage Server, Network Storage Manager, Virtual Tape Server, and Cross Platform Extension, can be combined into integrated storage solutions optimized for specific business environments.
Management: As SANs get larger and more complex, managing all the components becomes a greater challenge. Choosing the right management software is critical. A solid solution will allow SAN managers to control the entire storage network from a single interface and change the parameters of the network to address changing storage needs. Some software packages currently available include SAN InSite from Vixel and SANavigator from Connex.
Language support: When used for Internet-related purposes, support for different languages and character sets is vital. Users spread across a global enterprise, for example, may access information and use programs in many languages.
Price: The good news is that SAN and NAS solutions are becoming increasingly more affordable. However, creating a networked storage solution still requires a significant investment in hardware and software. At the low end, a NAS with four IDE drives and an 80-GB storage capacity costs about $4,000. The midrange, which often has six SCSI drives, costs about $12,000. At the highest level, NAS appliances incorporate about 10 drives, as well as redundancy and fault-tolerance features, and cost about $40,000. A midrange SAN is much more expensive, with average price tags reaching $250,000 and an average time for return on investment of between 18 months and two years.
Whether you're evaluating, designing, building, or buying a NAS or SAN solution, start simple and build up to a more complex environment as needed.
What kinds of NAS and SAN solutions are you considering?
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