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Network-attached storage (Nas) is a minority sport at the moment, but one whose popularity is growing rapidly, driven by recent improvements in the basic performance of the technology.
Suppliers have enhanced performance by building their products as appliances - devices designed for a specific task. So Nas systems now typically have their own purpose-built operating system that is optimised for file sharing and is unable to run any other application. An example is Network Appliance's Ontap, which contains just 350,000 lines of code.
This approach makes the systems easier to use; boosts performance by offloading a lot of the I/O traffic from the application server; and aids storage management through the use of software tools.
Nas was initially successful as a storage alternative for low-end networks. It developed into a serious storage solution for a much larger market with the emergence of storage area networks (Sans) and Internet-based computing, which has created a much larger requirement for file sharing.
Nas systems are very different from Sans, which are designed for consolidating the storage used by multiple servers. Sans are resource-sharing rather than data-sharing systems. Sans are typically built using Fibre Channel technology, which is significantly more expensive than Ethernet. They have their own set of standards, which are still under development. And they are much more complex, requiring skilled resources internally and usually some external consultancy expertise as well.
On the plus side, Sans offer a much higher level of performance than Nas systems because the Fibre Channel protocols were specifically designed for storage systems, whereas the Ethernet protocols used by Nas are general-purpose. Fibre Channel connections have also traditionally been much faster than Ethernet connections. Sans are much more scalable because they employ a switched fabric, whereas Nas systems use point-to-point connections.
Up until now, Sans have been installed by large enterprises with the resources to manage the huge data storage requirement which justifies the economies of scale a San provides. Nas systems have also been installed by large companies for specific purposes where file sharing is appropriate. For small and medium-sized organisations, Sans have provided an entry point to networked storage.
Thanks to two key technology advances, this picture is now changing. First, Ethernet performance is now significantly faster with the arrival of Gigabit Ethernet, and will soon get even quicker with 10 Gigabit Ethernet. Second, a new protocol, ISCSI (Internet Small Computer System Interface), designed for moving storage data over Ethernet, is currently under development.
Taken together, these two factors are opening up the possibility of Ethernet Sans. They will be attractive to small and medium-sized organisations that have been put off by the cost and complexity of Fibre Channel Sans.
Storage suppliers have moved on too. Up until 2000, the Nas market was dominated by small specialist companies such as Auspex and Network Appliance. The major storage suppliers were concentrating on traditional direct-attached storage and on the newly emerging Sans.
But the Nas companies have been very successful. Market leader Network Appliance had sold more than 17,000 of its Nas filer products. At the bottom end of the market more than 50,000 of Quantum's small Snap Nas systems have been installed.
Analysts companies Gartner Dataquest and IDC put the total size of the Nas market at between $1.5bn and $2bn (£1.04bn-£1.38bn) in 2000, and they are forecasting rapid market growth of about 60% a year for at least the next five years, leading to a market worth $6bn to $7bn by 2003.
With figures such as these it was not surprising that 2000 saw most of the major server suppliers decide to enter the Nas market. Sun introduced its Solaris-based Storedge N8000 in May 2000. Compaq launched its NT-based Tasksmart N-Series two months later. Hewlett-Packard joined in with a Nas version of the XP512. Dell came into the market in September with the 705N, which was based on a Quantum design, and then followed up with its own 735N product in February 2001.
IBM dipped its toe in the water in September 2000 with an adapted xSeries server, then entered the market seriously with the 300G Nas bridge in February 2001 and two purpose-built Nas systems in June.
EMC was an early entrant to the Nas market with its Celerra product in 1996, which provides Nas functionality using the existing Symmetrix disc subsystem. The company launched its first purpose-built Nas system, the Clariion IP4700, in December 2000.
This flurry of new product releases changed the marketing perspective. Up until this point, Nas and Sans had been promoted as directly competing alternatives by both Nas suppliers and traditional storage companies. But the industry has now adopted a horses-for-courses approach - Nas is good for some things, Sans for others. "Most organisations have a need for all the different variants - direct-attached, Nas and San", says Garry Elliott, Auspex's UK manager.
The recognition that Sans and Nas both have roles to play has also contributed to a blurring of the boundary lines between them.
For example, several Nas systems now use Sans for storage rather than their own dedicated discs. EMC's Celerra connects to a back-end Symmetrix-based San, and can be split between Nas and San. The IBM 300G is a similar product, also connecting IP network clients to San storage. More recently, Hitachi Data Systems has introduced Freedom Nas, which combines an HDS Thunder or Lightning storage subsystem with a Nas server, and can, like Celerra, be split between Nas and San.
Hewlett-Packard's Nas 8000, launched in March, can be either a standalone Nas system with its own storage or a Nas "head" (containing Nas functionality but no storage) connected to a San. Auspex has gone down this route too, introducing a Nas controller with San-based storage. "It will free up the 30% of storage on a San that people don't know they've got", says Elliott.
Another approach is the "soft" Nas system, providing Nas functionality for the user's existing storage hardware. This approach has been pioneered by Novell with Netdevice, which was launched in July 2001. The company says Netdevice will plug into any network and allows the use of any storage hardware. It is shipped as an integral part of Netware 6 but can also be bought separately. The product is selling well. "Where small offices use shared storage, so use of the Internet is impractical, Nas is ideal," explains Brian Green, director of Novell's Network Management Group.
Traditional Nas systems are also evolving. As in other areas of the storage market, capacities and performance are improving all the time. Performance has also been improved by the arrival of Gigabit Ethernet and of TCP/IP offload engines. More significantly, Nas systems are acquiring enterprise-class characteristics they did not previously have.
The Dell 735N has snapshot and mirroring capabilities. Network Appliance has also been adding mirroring software. In addition, it has improved the system's high-availability characteristics. EMC's Clariion IP4700 was designed with high availability in mind from the start, and has no single point of failure. IBM's Nas marketing manager Roger Messenger says, "We emphasise data protection as a major feature of the Nas 200 and 300."
There is now a move towards making Nas systems suitable for sharing databases as well as files. A major feature here is the development of the new file-sharing protocol Dafs (Direct Access File System). Network Appliance's Northern Europe SE director Stuart Gilks says, "Dafs will offer benefits especially in high-transaction, high-performance environments."
Dafs was announced June 2000, and is being developed by the Dafs Collaborative, an industry consortium of 80 members. Demonstrations of IBM DB2 and Oracle 9i applications running over Dafs took place in June 2001. The final specification was completed in October and is now under consideration by the Internet Engineering Task Force. Products implementing the protocol are likely to arrive soon, probably in the second half of this year.
So who should use Nas? Encouragingly, the range of applications is wide. Today it remains an option for specific enterprise tasks - "Where there is unstructured data that needs to be shared in file mode, with a requirement to share between many end-users," as EMC's Nas SE manager Mike Bradley puts it. Here the question is whether to use a dedicated standalone system or build in Nas functionality as an integral part of a storage network.
But the main application has to be consolidation. Look at Nas if you are in a small to medium-sized company that does not want the complexity of Fibre Channel Sans but does want the benefits of consolidation, whether in a file sharing context or not.
What is network-attached storage?
Network-attached storage (Nas) is a specialised form of networked storage that was initially designed for sharing files between graphics workstations. This historical background still affects the design of Nas systems today.
Nas is used for file sharing between computers running different operating systems and file structures. All Nas systems support the two most common file sharing protocols, NFS (Network File System) and Cifs (Common Internet File System). So Nas systems can share data between different kinds of Unix systems and between Unix and Windows systems.
Nas was the first type of storage system to offer genuine data sharing between different computers, as opposed to simply disc sharing.
Nas systems are attached to Ethernet local area networks, so installing Nas requires no new technical equipment or changes to servers - it is plug-and-play. Most Nas systems can be up and running within 30 minutes of leaving their boxes (or less).
Nas also requires no new expertise on behalf of technology staff - all the standards governing Nas systems are well-established and all the technologies are familiar.