Choosing the right storage solution for your network needn’t be an either/or choice between a SAN (Storage Area Network) or NAS (Network Attached Storage). In fact if you think the two formats are mutually opposed you’ve got it all backwards, so to speak. Geoff Marshall offers some advice on getting the best from both storage worlds

Last month we looked at the new concept of the Storage Area Network (SAN), which is often confused with Network-Attached Storage (NAS). Here we're going to explain the differences, focussing more on NAS.

The Data Explosion
By the year 2000, the estimated annual growth in demand for online data storage will be running at over 50 Petabytes (1 Petabyte = 1,000 Terabytes) with PC, UNIX and NT users generating over 90% of this. Companies are realising what an enormous data management headache this presents. Consequently, enterprise data storage is now a necessity as corporate information is moved to the strategic centre of technology operations. However, data is no longer restricted to a single host machine, but has moved to an open system, often in mixed-platform environments.
This proliferation of open systems, often involving many servers, PCs, and laptops has led to data being distributed across heterogeneous computer systems and networks. Business data objects no longer reside within single data architectures and consist of multiple information structures such as records, fields, text, images, or audio. Consequently, a data storage (or archiving) system must be able to support all data types stored on multiple platforms. Don't lose that data!
Data distribution has also created other problems, particularly in the areas of security, access and availability. Disaster recovery procedures and resilient data back-up routines are vital for organisations that depend on their electronic data for doing business -- we all know that any data loss could have catastrophic consequences, especially if the loss is irretrievable. This leads to the storage medium. Data backups and archives must be robust, safe and secure because users have a habit of wanting their data back at some point!
The future of tape looks assured -- or does it? Tape life is finite and users know they must backup their tape backups at least every two years before the medium starts to degrade. However, the short life of tape does mean that future sales of tape cassettes are guaranteed -to committed tape users. Likewise manufacturers are encouraged to continually develop tape drive technology. The logistics of storing tapes is labour intensive - changing cassettes, labelling, tape libraries, catalogues, physically moving tapes to safe, secure sites and the time to find and restore data can run into days!

NAS or SAN ?
NAS defines an open architecture for managing and consolidating data storage operations in today's corporate and enterprise networks. They are designed
to accelerate application performance, giving users shared data access in heterogeneous environments, as well as enabling administrators to consolidate
storage from multiple desktop and server systems into a centrally-managed pool of data. One of the issues surrounding SAN (described fully last month) is it's shortcomings in these areas:
• Data to desktop
• Heterogeneous data sharing
• Lack of standards for file access
and locking

The best of both worlds?
One company, Network Appliance, has combined the benefits of SAN and NAS (Network-Attached Storage) to produce a complete solution that gets away from such shortcomings. The new combined SAN and NAS architecture supports increased enterprise scalability and utilises existing industry-standards like TCP/IP and Fibre channel. Data sharing, storage management, backup and network administration become simpler and more effective, leading to reductions in total cost of ownership.
The latest report from IDC predicts the growth of the NAS market in excess of 55% per year through 2003. This IDC report also ranks Network Appliance number one in NAS revenue with 41% of the overall market share for 1998. We spoke to the UK Managing Director of Network Appliance, Steve Ronksley, who says, "The explosion of data in the work place has generated a strong demand for storage architectures that can solve the business problems of managing network accessible data. As the market leader in network attached storage, Network Appliance is focused on providing dedicated filers that deliver on our reliable, fast and simple appliance philosophy. The company's philosophy is to design specialised servers, called appliances, which are dedicated to particular data access and storage tasks, thus optimising performance, ease of deployment and manageability. These appliances deliver fast, simple, reliable, and cost-effective access to data stored in the network."
Dan Warmenhoven, the President and Chief Executive Officer of Network Appliance, believes that there is an increasing amount of confusion over the type of storage markets: "The industry is not about Network Attached Storage verses Storage Attached Networks - it's NAS plus SAN. SAN encompasses NAS."

Decisions, Decisions
If you're still confused about the difference between SAN and NAS, here's some more questions (and answers) that are often asked by network managers: Do I go for a SAN based solution, or for a NAS device? Is NAS a stop gap to SAN? Will there still be a need for NAS devices when SAN's mature? Will the same NAS device support my need for file serving as well as database application serving? How do I protect my data once it's on the NAS? These are just a few of the issues that face those considering these emerging storage technologies.
The Storage Area Network adds a new transport layer to the traditional client/server model between the application server and the storage. The benefits of separating an application between the client and the server with a LAN has been well demonstrated over the last two decades, but this model is starting to show the signs of ageing under the weight of the current explosion in data storage.
The SAN gives the adopter the ability to do traditional storage management tasks such as backup and restore, clustering and replication without impacting the LAN or any of it's servers, and also opens the way for true device and data sharing on a scale previously thought impossible. Hence SANs are, in the short to medium term, thought to offer a server-to-server, server-to-storage or storage-to-storage solution. Put more simply, they are aimed at the back-end datacenter. Clients will still run applications across the LAN, with the application servers accessing their data across the SAN.
A NAS or Network Attached Storage device however, combines traditional disk array technology with ‘intelligence’. This intelligence is achieved by adding a small processing unit into the same case as the disk, which is commonly based on an Intel or SPARC RISC chip. In this way, the disk array can be attached directly to an Ethernet based network. We are all familiar with the idea of a network printer - a printer that anyone with the correct rights in the network can print to. The NAS device follows the same principle. It is a disk that is shared out over the Local Area Network using conventional file sharing protocols such as NFS or CIFS, to all the users with appropriate rights within the network. All the users in the network are able to mount filesystems directly from the NAS across the network without having to route the data via a server.
NAS devices raise a new set of challenges for storage management vendors. For example, how do you integrate a NAS device, or even a farm of NAS devices into our traditional backup and restore plan? If NAS devices are not directly attached to any server, how are we able to transfer data from the NAS to the backup server which has the tape storage sub-system attached? NAS devices tend to store in the region of hundreds of gigabytes, through to tens of terabytes of information, meaning that even if you have just invested in the latest gigabit Ethernet network, it is a huge amount of data to shovel across the LAN to a backup server. Having off-loaded the disk-based storage from your server, wouldn't it be a good idea to also move some of the relevant tape-based storage?
We spoke to Jonathan Martin, EMEA Product Marketing Manager at Veritas Software Corporation, about this NAS problem: "Veritas has taken a pivotal role over the past two years in the definition of a new industry standard protocol, which concerns itself with just this issue. NDMP, or the Network Data Management Protocol, which allows you to connect a tape library directly to the back of the NAS device, and drive the management of this tape library from your Veritas NetBackup server. By sending a new set of NDMP control commands from the Veritas NetBackup server to an NDMP-compliant NAS device, data is moved via SCSI from the NAS disk to the tape library, while the metadata (what got backed up, where it got backed up to, etc) is stored on your Veritas NetBackup server as usual. In this, way, you are backing up large amount of consolidated data, without impacting the production servers that are using that data.
"The level of intelligence that is built into the current crop of NAS devices wouldn't notch up anything Einsteinian in an IQ test, but they do give you the basic ability to consolidate data into a central storage resource, and make it available to a wide number of users. Veritas is working with a number of it's strategic vendors on a second generation of NAS devices, something that Veritas is branding an iNAS (or intelligent NAS) device. It is only a small step to make from running networking software on the NAS CPU, to running other applications. In this instance, we are talking about a stripped down set of the classic Veritas storage management technologies such as Veritas File System, Veritas Volume Manager and Veritas NetBackup. The management of the storage is therefore no longer driven from the server, but is housed on the storage itself freeing up the ever more precious CPU time on server for its applications.

Conclusion
Both SAN and NAS devices have a valid part to play in the evolving storage market, and require a different approach to managing them. See http://www.ndmp.org for more details of the Network Data Management Protocol.

Steve Ronskley: A strong demand for storage architectures that can provide network accessible data

Above : The F760 Tower from Network Appliance

Jonathan Martin: NAS CPU’s can be made to run applications other than networking software