NAS gateways converge SAN and NAS, enabling storage consolidation and a single pool of storage to manage.
By Michele Hope
The debate about networked storage architectures at the enterprise level no longer centers on the SAN versus NAS controversy. As organizations have begun to reap the benefits of consolidated storage, the question has now changed into how to blend or "converge" networked storage technologies to achieve the best of both block- and file-based storage.
This trend toward SAN-NAS convergence in the data center has an ultimate goal of allowing data centers to centrally manage and scale all of their IP-based file-level storage as a component of an existing, block-based Fibre Channel SAN environment.
One of the most common examples today of SAN-NAS convergence is the use of NAS gateways in data-center environments. Basically derivatives of integrated NAS appliances, NAS gateways sit in front of a SAN and use the SAN's block-based storage resources for file-based storage access as well.
When embarking on this type of converged or hybrid architecture, you should know the benefits you hope to gain from this move and the right questions to ask of vendors who operate in this space.
Dissecting NAS gateways
To understand how NAS gateways work, you should first look at the operation of integrated NAS devices.
Integrated NAS appliances house both a front-end and back-end component: The front-end of the appliance-often referred to as the "head" or "brains" of the device-is the CPU/controller function that processes file-level storage access requests made from network clients via file-sharing protocols such as CIFS and NFS. The NAS appliance back-end, or "body," consists of the hardware device or storage array where file data is stored and accessed.
In contrast to appliances, NAS gateways decouple the connection between the brains and the body of an appliance. Instead, they offer just the front-end NAS head or controller component to process file-level requests. The gateway then relays and translates file-level requests to the various block-based storage devices attached to the SAN.
A primary motivator for using NAS gateways in the data center is their ability to bridge the gap between the file-based storage needs of an organization's IP-based client network and the robust block-based storage capabilities of a Fibre Channel SAN.
Hewlett-Packard, which offers a line of Windows-based NAS gateways such as the 4000S and 9000S, has coined the term "NAS/SAN fusion" to describe this type of hybrid file- and block-based storage architecture. (For a Lab Review of HP's NAS 9000, see "Turning shared blocks into shared files," InfoStor, October 2004, p. 42.)
According to Ian Duncan, worldwide NAS marketing manager at Hewlett-Packard, the primary reason for NAS gateway adoption among the company's enterprise IT customers is the desire to consolidate storage resources by eliminating disparate pools of file-level storage that exist throughout their IP networks. "The number-one reason why customers are going this route is to eliminate their islands of storage," says Duncan. "When you have a NAS gateway, you can serve both block- and file-level storage out of the same storage pool."
NAS gateways appear to be making inroads into enterprise data-center environments precisely because of their ability to aid in a company's storage consolidation initiatives, according to Randy Kerns, an enterprise storage analyst and senior partner at the Evaluator Group consulting firm. "Gateways have huge benefits for environments that have an existing SAN and that are being told to get their file servers under control," says Kerns. "Gateways are a good solution for enterprise data centers that need to do file-server consolidation and want to use their existing resources."
Tom Joyce, senior director of NAS product marketing at EMC, which offers a range of NAS gateways along with integrated NAS servers, reiterates the consolidation lure that often accompanies NAS gateways. "A key driver for customers getting into NAS gateways for the first time is saving money by consolidating [their servers]," says Joyce. "Customers look at server requirements and may say, 'I'll be adding 20 servers a year over the next few years. If I can avoid doing that [through the use of gateways], that saves some money and reduces the number of things to manage.' "
The ability to consolidate and streamline backups for file-based storage may be reason enough for NAS gateways, according to Brad Nisbet, program manager for storage systems at International Data Corp. (IDC), a market research firm. "The idea is to consolidate all of your file-level services to a separate pool of storage. You don't have to back up 10 servers anymore. You can now just back up one NAS device. If you converge NAS and SAN with a gateway, you only have one pool of storage to manage and back up," Nisbet explains.
EMC's Joyce confirms the growing popularity of NAS gateways among EMC's clients and reports that gateways now comprise the majority of EMC's NAS shipments. "Some customers may start by looking at an integrated NAS system or appliance. But then they start saying, 'What if I want to use a SAN two years from now?' They may opt for a gateway instead, along with a small Fibre Channel switch and storage array. This gives them the flexibility to change those three components out or move things around."
IBM entered the NAS market about three years ago with both a NAS gateway product and an integrated NAS appliance. At the time, they weren't sure which product would strike the best chord with customers, says David Vaughn, worldwide product manager in IBM's storage systems division. "We didn't know whether they'd want the packaging of an appliance or the flexibility of a gateway," says Vaughn. "At the high end, what happened was dramatic. By about six to one, our customers preferred the flexibility of a gateway over an appliance."
Increasing storage utilization rates
One user elaborates further on the benefits his group has achieved through the addition of NAS gateways in an enterprise storage environment. "If we didn't have a gateway, then we would need to have two separate sets of storage. It would also require two separate labor pools to manage," says Michael Forman, group director of North American IT for Cadence Design Systems, an electronic design automation (EDA) software company in San Jose, CA.
Forman is responsible for Cadence's global storage, which includes about 400TB across the world, 250TB of which is stored on what Forman calls production-quality servers from Network Appliance and a set of monolithic, 10TB to 22TB SAN Enterprise Storage Server (ESS) arrays from IBM. Forman's group currently uses five gFiler gateway clusters from Network Appliance at the front of several of its 15 ESS systems.
Besides easier management of a single storage pool, Forman notes that the use of gateways has also allowed his IT organization to achieve significantly higher disk utilization rates.
"Our disk utilization rates have always been in the 90% range using this SAN/NAS gateway," Forman says. "If we had a separate SAN or NAS solution, there might be one side that had excess disk capacity. But, if you were on the other side, you couldn't take advantage of it. You become much more efficient in terms of disk utilization when you share NAS and SAN."
Postponing forklift upgrades
Perhaps the most unique benefit Forman has been able to derive from the use of NAS gateways, however, involves his plan to postpone the more-common, forklift upgrades of his back-end IBM disk arrays from once every three to four years to what he anticipates could be as much as once every five to seven years.
"Most companies replace their entire storage solution every three or four years," according to Forman. "We expect to extend the life of our ESS systems from five to seven years just because we are upgrading the front-end [gFiler] technology. With this hybrid solution, we plan to just upgrade the front-end every three to four years."
HP's Duncan notes that scalability and the ability to accommodate future expansion plans have also been key to the attractiveness of NAS gateways. "Now you have NAS being able to scale to the limit of a SAN."
Flexibility and expansion capabilities-including the ability to expand its storage capacity and the number of attached users-are just two components that help make the gateway concept so attractive to data centers, according to Rob Gallini, architecture manager of IT services at Meijer, a company that operates a chain of US-based grocery stores and super centers. "The flexibility of the NAS heads [gateways] on top of a SAN are vital to a corporate data center," says Gallini. "[Traditional] NAS units do not offer the expansion and configuration flexibility that we need."
Meijer is in the early stage of its rollout of an HP SAN that incorporates an HP StorageWorks Enterprise Virtual Array (EVA) 3000, coupled with two HP B3000 NAS gateways on the front of the SAN. The gateways are currently configured to handle the client workload of several thousand users at Meijer's 150 stores throughout the Midwest.
The market for integrated NAS is expected to grow at a 10.4% CAGR, while the market for NAS gateways is projected to grow at a 40.3% CAGR through 2008. Projected CAGR for the overall NAS market is 14.8%.
In terms of gateway performance, some users also note significant improvements in file-level transfer times and file access speeds for extremely large files. "It's like a rocket now," says Raymond DeCrescente, speaking of the speed at which the company's NAS gateway now allows users to access files, such as the large digital X-ray files produced through the Picture Archiving and Communications System (PACS) at the Capital Region Orthopaedic Group, an 18-physician practice in Albany, NY. DeCrescente, the CTO of the group, oversaw a complete overhaul of all of the company's storage infrastructure a few years ago that included two HP B3000 NAS gateways and 9TB to 12TB of storage capacity in an HP StorageWorks EVA 5000-based SAN.
"The surgery center upstairs used to have a standard server that ran their applications. Now they say downloads and producing reports are twice as fast as they used to be," says DeCrescente.
Judging by the increase in recent gateway sales, the merits of NAS gateways are not going unnoticed among enterprise IT professionals. According to Nisbet, IDC believes that NAS gateways will make up as much as 25% of total NAS revenues by 2008. He also expects NAS gateway sales to grow at a compound annual growth rate (CAGR) of 40.3% through 2008. In contrast, he estimates the CAGR for integrated NAS to follow a much more modest growth curve of 10.4%.
Do your homework
Before purchasing or implementing a NAS gateway, consultants and users agree that it pays to consider a few areas ahead of time:
Management software: Who manages whose stuff? According to analysts Kerns and Nisbet, you need to make sure that your SAN management software will work well with your NAS gateway management software. Kerns says you should ask whether you can still take advantage of the tools you're using today to manage block-based storage. For example, if you're connected to an IBM ESS, you should ask yourself if the management of the ESS is going to be the same once you add a gateway, or if you'll have to use a different host. Nisbet says you should ask yourself, "Can I integrate what I need to do with the file-level servers on the NAS gateway with the management level software that exists for the SAN?" In most cases, he says, your answer will likely be, "Yes," but it's still a good move to check this out ahead of time.
Heterogeneous mixing and matching. Most vendors that offer gateways as part of their overall storage offerings admit that the majority of their NAS gateway customers are not interested in adding the company's gateway to some other vendor's back-end storage. However, Network Appliance tends to disagree with this type of blanket statement. According to Jeff Hornung, vice president and general manager of NetApp's gateway business unit, asking if the vendor's gateway is truly a multi-vendor gateway is an important question for users. Why? "It gives users a way to pull together existing vendors' storage that they have in their organizations," he says. IDC's Nisbet says the prevailing trend among NAS gateway vendors is to offer their gateways only for use with their own SAN storage products. He doesn't see this trend changing much in the near future, either, as vendors continue to favor homogeneous solutions for NAS gateways. He concedes that Network Appliance, Hitachi Data Systems, and IBM are exceptions to this trend, due mostly to the partnerships NetApp has with the other two vendors.
Gateway sizing considerations. When implementing NAS gateways, you should do some up-front legwork to determine the maximum number of users and average client workload that a NAS gateway can support. From the Network Appliance gFiler perspective, Cadence Design Systems' Forman recommends putting in a cluster and making it available at first to only certain business groups. Then, slowly add in other groups while monitoring how the system is handling peak and normal client workloads.
"If you have spare capacity, you can keep adding groups until you reach a reasonable saturation point," Forman explains. "Every company has to determine what [saturation point] they are comfortable with. On average, we try to target around 70% average load per head." Hewlett-Packard's Duncan says HP offers a Network Storage Solutions (NSS) "sizer" tool that helps users determine which storage systems, including NAS gateways, are right for their environment. In terms of NAS gateways, you'll be asked questions such as the number of peak concurrent users you anticipate will access the gateway, the capacity requirements of the workload group, the read/write ratio, throughput requirements per user, and preferred RAID levels.
Michele Hope is a freelance writer and owner of TheStorageWriter.com. She can be reached at firstname.lastname@example.org.
Xiotech combines NAS, SAN
Xiotech last month added a NAS appliance to its line of Magnitude 3D SAN arrays, allowing users to combine file and block services in an integrated configuration. The Magnitude 3D NAS is implemented as a stand-alone appliance that connects to the company's disk systems via Fibre Channel.
The appliance is based on Microsoft's Windows Storage Server 2003 software and includes support for Microsoft's Volume Shadow Copy Service (VSS) and Multipath I/O (MPIO).
"The number-one reason [for NAS-SAN convergence] among our users is consolidation of servers and storage, as well as site consolidation," says Rob Peglar, vice president of technical solutions and chief market technologist at Xiotech.
The NAS appliances, which include eight Gigabit Ethernet ports and support for CIFS and NFS, can be clustered. In addition, users can schedule snapshots (point-in-time copies), assign shares, reconfigure storage, and replace disks online.-DS