Published: 17 Nov 2002
Data demands placed on businesses continue to grow and IT managers are responding by expanding storage, both in storage-attached networks (SAN) and network-attached storage (NAS) solutions. But this two tier approach, which balances performance, reliability and cost to suit specific missions, comes at a growing price. IT managers must manage two or more distinct and incompatible storage infrastructures, inviting spiraling costs and complexity.
Over the past 18 months, software and hardware vendors have released solutions aimed at closing the gapbetween block-based SANs and file-based NAS solutions. While none has bridged the SAN/NAS divide, the FAS900 series of converged devices from Network Appliance comes close. The FAS960 and FAS940 products offer in one box the file-based I/O functionality of NAS devices and the block-based I/O capability of SAN solutions. More importantly, the FAS900 series offers a unified environment, providing a common management console and dynamic allocation for both block- and file-based storage.
In effect, Network Appliance is promising seamless integration of both NAS and SAN storage. Network Appliance's motives are easy to understand: The Yankee Group estimates that at $7.44 billion, SAN revenues will triple NAS revenues this year and still more than double them in two years. The attraction for users, however, is a device that's more flexible, yet easier to manage, than a dual environment.
|Bringing file and block together|
"You can run blocks for those applications that absolutely require block I/O. And you can run file I/O as well and eliminate a whole bunch of servers," says Alan McLachlan, senior systems engineer for integrator ASI Solutions in Sydney, Australia. "Not only do you get more users per server. You can get rid of a whole bunch of servers."
But initial reports suggest that storage managers are not likely to adopt the Network Appliance approach to meet all of the demanding performance and reliability requirements of today's SANs. Rather, it will find favor for important parts of the storage infrastructure ill-served by current technology.
Network Appliance isn't the first vendor to offer NAS and SAN connectivity in a single device. Products like the EMC Celerra, the IBM 300G, and NetApp's own F860 and F820 filers can connect to clients and servers via Ethernet on one side, and to a SAN-based disk array over Fibre Channel links on the other. These so-called NAS gateways, or NAS heads, allow IT managers to house all data-be it file- or block-based-on a single array of disks on the SAN. Consolidating disk storage around a single platform can help cut disk procurement costs and whittle down complexity.
The bits behind a NAS gateway may reside on a common physical platform, but still manage and access those bits distinctly. NAS-based storage occurs on specifically demarcated disks, with accesses traversing both the NAS device and the SAN. SAN accesses, meanwhile, bypass the NAS gateway entirely. Unfortunately, the additional layer adds complexity and introduces bottlenecks on the NAS side. More important, IT managers must employ distinct management consoles and tool sets to manage NAS and SAN-based data and resources.
The FAS900 series overcomes this by unifying the physical and logical storage environments in one device (see "Bringing file and block together"). As with NAS gateways, all storage resides on the SAN disk array. But where NAS gateways provide a portal for file-based I/O into the SAN array, the FAS900 series serves as the common access point to the array for both NAS and SAN operation. To do this, the device provides native block and file based I/O inside the device.
"One of the reasons I think this is an interesting system is because it allows the customer to take advantage of their infrastructure," says Mark Santora, vice president of marketing for Network Appliance. "They can move storage from IP to Fibre Channel at will. They don't have to copy and move data around. Just take that disk, move it over there, and boom."
Thinking inside the box
Much of the converged functionality is found in Network Appliance's Data ONTAP 6.3 software, the operating system inside the FAS960 and FAS940 devices. At the core of Data ONTAP is NetApp's Write Anywhere File Layout (WAFL), file system. WAFL was designed as an extensible file service that can natively implement multiple protocols, including NFS, CIFS and HTTP.
NetApp achieves SAN/NAS integration by extending virtualization already present within the operating stack. While NAS devices virtualize disk access by filtering application calls through a file system, SANs access the physical disk interface. Virtualizing the disk interface and cache management layers for both file and block I/O operations allows NetApp to put both SAN and NAS functionality in a single package.
Randy Kerns, senior partner at storage industry research firm The Evaluator Group, says the approach is a smart one. "What they've done is put another abstraction layer inside their operating system to handle the different interfaces for remote file serving vs. block access for Fibre Channel. But everything underneath is the same software they've had previously in their filers."
|NAS or SAN? Consider this|
The virtualized approach promises to resolve some of the thorniest SAN management issues, including rigid volume handling and troublesome LUN assignments. The FAS900 series layers LUN management over the storage virtualization layer in the stack. This allows the FAS900 series to deliver to SAN-aware applications and utilities the information they expect, while preserving a rich, hybrid environment on the back-end disk array. Buffer caching, RAID management and disk management all occur behind this abstraction layer.
Santora stresses that all protocols - including SAN protocols - are supported natively in the Network Appliance stack. Rather than emulate protocols, the FAS900 devices work directly in the protocol itself. The abstraction layer handles translating calls to and from the disk array.
"Our Windows interface is at the data level. If you want a Windows only system, you can get one from us, it's native. If you want an NFS or Unix implementation, you can do that. It's native. The same thing with Fibre Channel, it's native. If you want to build a Fibre Channel SAN with my system, go ahead."
A matter of focus
Not every SAN player is impressed by what Network Appliance is promising with the FAS900 series. EMC spokesman A.J. Ragosta contends that the one-stop-shop approach in the Data ONTAP operating system waters down functionality and exposes multiple single points of failures in the new appliances.
"I'd say what NetApp is doing is surf and turf for storage," says Ragosta. "You have one processor running two very different functions and trying to do them both well. You are getting an OK piece of steak and an OK piece of fish."
Ragosta contends the FAS900 architecture lacks redundancy and availability features critical to a high-stakes SAN environment. He singles out the pointer system used by Data ONTAP to establish the location of files written to disk. A power failure or other disruption during a write operation could force users to take both the NAS and SAN offline while re-establishing lost pointers.
"Any time there is a problem with the NAS and you take it down to fix it, you are taking down your SAN as well, and vice versa," Ragosta says. "There's another vector of potential failure. If one has any kind of problem that needs maintenance, you're affecting performance and availability for your other solution."
Kerns agrees that the current FAS960 and FAS940 devices won't find their way into data centers today.
"For the customer, it's just another SAN solution," Kerns says. "But it's a complete SAN solution-a SAN in a box-in that the interface and controls are all in one package. What they did makes perfect sense."
Kerns expects the FAS900 line to get early traction in the area of Windows consolidation, enabling managers to deploy a simple SAN to replace hard-to-manage NT file servers using direct-attached storage. Consolidating the Windows environment has some challenges. While most such environments are file-intensive, and therefore good NAS candidates, newer versions of Exchange Server and SQL Server are not NAS friendly. Integrated SAN/NAS capabilities are one way to address that problem.
Broadcom Corp. is a case in point. The maker of chips for broadband devices stores the majority of its data on a variety of NAS devices from Network Appliance. The company also manages a SAN, which is used to provide block-level access to SQL Server and Exchange.
"The new product line, from a SAN/NAS convergence perspective, allows me to start tearing down the one SAN implementation I have going here," says Ken Venner, vice president and CIO of Broadcom. "I just personally prefer the ease of implementation and use of NAS. Though with this particular product we're going to take a look at this to see which direction we'll go moving ahead."
While Venner may have a preference for NAS, what about traditionally demanding SAN environments? Critics wonder if loading on the NAS side of the device might degrade performance on the SAN side, and vice versa.
Arun Taneja, senior analyst with Enterprise Storage Group calls the performance issue "totally open right now," citing the lack of comparative SAN benchmark results.
As for file performance, published NAS benchmarks, seem to show impressive scalability in the FAS900 line. The SPECsfs97_R1.v3 benchmark published by the SPEC Organization, reveals that the number of operations per second more than doubles when comparing the FAS940 to NetApp's older FAS825. Performance more than triples on the FAS960.
Rick Hulsey, system design engineer at Southwest Airlines, says his team has gotten similar results from internal benchmarking. Southwest Airlines has deployed a cluster of FAS960 devices and expects to add more as storage demands grow. Hulsey credits the Network Appliance WAFL file system for the impressive results.
"Unless you get a very large number of disks and make a lot of very wise choices about striping the data, you'll have a very difficult time optimizing the file system better than WAFL does it," Hulsey says.
Yankee Group Senior Analyst Jamie Gruener expects Network Appliance will challenge SAN leaders like EMC, Hitachi Data Systems, and Hewlett-Packard. Simplified management, a more open solution set and the prospect of sharply lower total costs of ownership make Network Appliance a vendor to be reckoned with, Gruener says. The strategy that should get some traction with budget-strapped IT managers seeking lower lifecycle costs.
Jerome Wendt, senior SAN analyst at First Data Corp, says the cost of managing storage far exceeds procurement costs. "For every dollar you spend on storage, you are going to spend another seven dollars managing it."
The unified management interface of the FAS960 and FAS940 may offer IT managers a way to shave that figure. Because the Network Appliance devices treat block and file level I/O in exactly the same way at the disk interface, the same software can be used to address both NAS and SAN management.
Filling the holes
One area where Network Appliance has a lot of work ahead is in interoperability. At the launch, the company announced an OEM agreement with Fibre Channel switch maker Brocade Systems to integrate its products into the FAS900 series solution set. The agreement includes both the 2 Gb/s Brocade SilkWorm 3800 Enterprise Fabric Switch and the SilkWorm 3200 Entry Fabric Switch. The deal is a critical one for Network Appliance, which needed to show it is ready to deliver a complete solution to SAN customers.
Network Appliance also announced extended partnerships with Veritas and Oracle, with the aim of illustrating its commitment to providing full-line network storage solutions. But with operating system support limited to Microsoft Windows and Sun Solaris, it's clear Network Appliance has work ahead of it.
It's early yet, but Gruening expects Network Appliance will deliver on its promise to turn the FAS900 series into a supported SAN/NAS convergence solution. "It's not in [Network Appliance's] best interest to make this a lock-in strategy. They are saying to their customers that whatever you have in there at the storage management layer we can work with," Gruening says. "This is like the first chapter of a new book for them. I think they are gunning for the data center, but they are doing it in a way that is a very tiered approach."