When it comes to serving up files to meet the demands of applications and network users, traditional file servers...
are too small for many of today's businesses, and large storage area networks (SANs) are too expensive and too complex. The gap between traditional file servers and SANs is being filled by network attached storage. NAS technology provides powerful file serving capability, high storage capacity and a growing suite of enterprise-class features.
Having emerged as a primary storage resource in small and midsized businesses (SMBs), NAS is now proving itself in the enterprise. "Every one of those Fortune 200 companies has some form of NAS file sharing -- whether it's an appliance or Windows file serving in their organization," says Greg Schulz, founder and senior analyst at the StorageIO Group.
This article covers the basic concepts of NAS as well as NAS implementation issues, and shares several real-life NAS case studies.
NAS basics In its simplest form, NAS is a disk-based storage system with an IP network interface for serving files on an IP network. This dedicated file serving offers vastly greater storage capacity than traditional file servers that hold just a few disks. NAS is also noted for superior connectivity and storage performance, allowing applications and users to be serviced faster and more reliably than common file servers. A NAS system is simple to deploy, requiring little more than a power source and an IP network connection for basic operation. A proprietary operating system is frequently included to enhance performance and ensure security. NAS is recognized for three principal benefits: consolidation, deployment simplicity and ease of management.
Before NAS, hundreds or even thousands of individual file servers might have been scattered throughout an enterprise, each with a few disks, each demanding maintenance or configuration from IT staff. Today, a NAS system can replace an array of file servers,
consolidating terabytes of storage into a single system at one location.
Some NAS systems now support dual-parity RAID (RAID-6 or RAID-DP) to guard low-cost SATA storage against multiple simultaneous disk failures. NAS administrators can easily install more disks to add storage capacity, and if the NAS box fills to capacity, a new NAS box can be connected. The consolidation and management of NAS resources can typically be managed with just one management software tool. This management software can often support multiple heterogeneous storage systems, further reducing management overhead.
NAS usually takes on the role of low-end storage, while Fibre Channel (FC) SANs are associated with high-end performance. However, this segmentation is changing because of faster Ethernet and better NAS design. The cost advantages that NAS has enjoyed "has inadvertently pigeonholed NAS to be perceived as cheap 'toy' storage, not befitting an enterprise," Schulz says, noting that contemporary NAS systems can support the storage tiering, high performance and high availability that had only been available in SANs. Although we often refer to NAS as a dedicated appliance (e.g., a NAS box) with its own internal storage, some organizations choose to forego a new appliance when a SAN already exists in the enterprise. Rather than a NAS appliance, they can use a NAS gateway to serve files from SAN or some other external storage. The presence of a gateway adds NAS functionality, but uses the SAN or separately attached disk array for actual storage. The advantage of a gateway is that NAS storage is not limited by the capacity of the appliance itself, but by the storage capacity of the separate array or SAN, which can be considerably larger. For more on NAS appliances and gateways, see the NAS Upgrades Buying Guide. Today, SANs remain the preferred choice for block-based storage in the enterprise, but NAS has become a staple of file storage, especially in its ability to serve unstructured file data. NAS can exist alone, but SAN and NAS technologies can coexist when the storage environment handles a mix of block and file data. "In a large environment, every good SAN should have a NAS, and every good NAS should have a SAN," Schulz says. Implementing NAS Implementing NAS typically involves the deployment of an appliance or gateway device, along with the configuration/management software. Most NAS deployments are turnkey, requiring only simple setups for basic operation. High-end NAS systems can be more complex and involve backup, replication and snapshot software. If you're deploying a high-end NAS system, you should note what functionality is available out of the box, and which features may require a separate software purchase. Keep an eye on the NAS network traffic. Without adequate bandwidth, a network segment hosting the NAS can easily become overloaded and impair performance. In most cases, a NAS is implemented with multiple Gigabit Ethernet ports that can be aggregated for improved bandwidth. Multiple ports also allow for failover, an essential element of high-availability operation. Performance is also a serious issue when the NAS is called upon to handle transaction-centric applications, such as databases or email systems. SANs are still the preferred choice for storage in heavy transactional environments, but high-performance NAS systems offer alternatives when the application workload can be balanced with the NAS system. "You start to run into limits with NAS at the very high end where you're serving up hundreds or thousands of database transactions per second," says Phil Goodwin, president of Diogenes Analytical Laboratories Inc. Highly intensive OLTP environments can have trouble being hosted on NAS, he nogtes. As an added wrinkle, NAS can sometimes influence software support. For example, some block-based applications may not even support deployment on file-based storage, so be sure to review the applications that you intend to host on NAS and verify that the application vendor will continue to support them. Lab testing is a good way to see the application's behavior and stability on a NAS prior to a major rollout. Managing a NAS system usually doesn't take much work, and good tools can ease the overhead. Opt for tools that will support multiple NAS systems and heterogeneous storage systems if you can. This way, the IT staff won't have to deal with multiple management tools as more NAS systems are added. Otherwise, the ease of NAS deployment can lead to a myriad of NAS systems and file servers, and the sheer number of NAS systems will ultimately lead to management headaches. "In the PC and server world, the solution is some sort of consolidation or virtualization," Schulz says. "We're going to start seeing more of that [virtualization] in the NAS space." Impact of NAS NAS can help companies overcome the expense of a SAN or the management headaches of DAS. NAS overcame both issues for Jeremy Whaley, director of information systems and network services at Claremont McKenna College in Claremont, Calif. Several years ago, the college used an IBM SAN with 4.5 TB, with another 3 TB spread out between DAS systems connected to servers as needed. The high cost of server HBAs left the SAN poorly utilized. "Only a handful of Windows file servers were taking advantage of the SAN," Whaley says. SAN performance was also a problem; frequent SAN reboots interrupted service to users across the campus. Whaley's challenges were to improve storage performance while keeping costs in line, and to begin a process of server consolidation that would support more storage on fewer platforms, while eliminating the security and patch headaches that accompanied a proliferation of Windows file servers. The college opted for the simplicity of IP network connectivity. "We knew we needed to fix, replace or redesign the storage facilities for the future," Whaley says. "The reason that we landed on NAS rather than another SAN is because we wanted to actually retire and consolidate our file servers -- of which there were many."
After about six months of consideration, the college settled on a Titan NAS system from BlueArc Corp. Whaley notes that BlueArc also supports iSCSI, so there is always a potential to add an iSCSI SAN later.
Whaley migrated the SAN data to NAS using the Robocopy utility. Testing and final activation took place in December 2006. There were numerous technical issues to resolve with network segmentation, but the deployment of the NAS itself was problem-free, says Whaley.
Today, the NAS provides 19 TB of usable storage to the college. Retiring individual file servers has reduced server management and maintenance issues, eased network congestion problems and improved storage reliability. "After we cut over [to the NAS] we continued monitoring the two side by side, and the old SAN has already had three errors where we would have had to schedule maintenance in the evening with IT staff on campus," he says. He also notes that remaining file servers have been very stable.
More storage will undoubtedly be added to the NAS system into the future, but Whaley is also considering a move to virtualize the remaining file servers, further consolidating the infrastructure. Beyond that is the prospect of disaster recovery, and that is where the replication feature of the Titan NAS system comes in. Whaley says, "If you have a second unit out there, you can replicate between the two in several different fashions." Healthcare providers have been increasing their raw storage to keep up with the demands of digital medical imaging. The Capital Region Orthopedic Group in Albany, N.Y., struggled with outdated practice management and surgery systems offering only about 200 GB of usable storage. With the move to a new facility in 2000, the adoption of an updated practice management system and a shift from conventional film to digital X-rays in 2003, the group's storage demands exploded. "We went from a mom-and-pop shop to an enterprise almost overnight," says chief technology officer Raymond DeCrescente, Jr. The incessant need for storage drove the adoption of a Hewlett-Packard SAN. An HP b3000 NAS head accesses a current total of 8 TB SAN storage for the group's updated picture archiving and communication system (PACS). Each digital X-ray study requires 25 MB. "We basically are filling our storage now at 5 GB per day," he says. The choice of vendor came down to a matter of convenience and capability. DeCrescente notes that access to local HP engineers and their ability to redesign a data center from the ground up were critical factors. This single-source approach avoided the need to tackle numerous storage and infrastructure upgrades through separate vendors. DeCrescente is particularly pleased with the scalability of his storage, noting that current 144 GB drives can be upgraded to 300 GB FC drives. This essentially doubles the storage to 25 TB. By installing additional drive shelves, the SAN can support over 50 TB. "I'm planning on doing just that, and then I can do disk-to-disk [D2D] snapshots," he says. It took about a month to test and burn in the new infrastructure, but DeCrescente is pleased with the reliability and call-home capability of the storage. Although he cannot quantify the return on investment or other financial impact of his storage choices, the benefits are clear. "You can't help but to save time on the maintenance." The one bit of advice DeCrescente offers is to take full advantage of training opportunities. "If I look back on it, I would have done that training during that month while everything was burning in." After DeCrescente adds storage, he intends to add HP data protector and snapshot software for enterprise-class data protection. A hardware refresh is planned in another several years, which will move the current SAN and servers offsite and install a new HP SAN in the main office -- allowing for D2D disaster recovery. Future of NAS Experts agree that NAS has a bright future in all types and sizes of enterprise, noting that NAS technology is evolving to meet more demanding tasks. Traditionally, NAS is deployed to support file-based applications in light-to-moderate traffic storage environments. But today, NAS use is expanding down into the small office/home office (SOHO) and up into the enterprise, and the lines between block and file storage are blurring. More block applications are being deployed on NAS systems where they would have appeared on SANs in the past. NAS systems are also increasingly capable of handling database and other traffic-intensive applications. Such improvements are often matched with better management tools and high-end features, like replication and snapshots. "There are some very large companies that run almost exclusively on NAS," Goodwin says. "As it becomes more capable, as people deploy more gateways and provide virtualization to their environment, NAS will continue to expand its presence."