As the volume of data generated in business grows, it becomes increasingly difficult to manage data and storage subsystems. A storage architecture is the solution, but how do you choose the right one for your enterprise?

Information may be a prized business asset, but what's the use of having it digitized and stored away if one can't access it when it's needed most? Organizations store data on various storage subsystems scattered across the enterprise. So locating a specific piece of information may be a tedious and time-consuming process. Managing multiple storage subsystems can be a harrowing task for network administrators. Another problem is the growth in the volume of data that's generated as business expands. The solution to all this is a proper storage architecture that provides for scalable systems, integration and management of storage subsystems. The solution should also offer data security, protection and recovery.

The acquisition of storage needs to be more than just a disk or tape purchase. Your network should graduate to accommodate the storage architecture and function as a whole.

Part of laying a foundation to a storage solution is to understand the kind of OS (Operating System) environment and the technical architecture that defines how storage is connected to the servers that execute the different enterprise applications.

INTEGRATION
Storage solutions should integrate well with OS environments. The various flavors of Unix and Windows NT/2000 represent the open systems area. There is a lot of diversity in these systems and many hardware and software solutions may not interoperate in all these environments. The current versions of NetWare, Windows, and all Unix variants have good support for storage integration.

For instance there's HP UX 11i, which integrates well with HP's storage systems.

Third-party storage software (like that offered by Veritas) should also integrate well with the operating system.
One should also consider storage architectures such as HP's ENSA-2 (Enterprise Network Storage Architecture), HP's FSAM (Federated Storage Area Management) and IBM's SSA (Serial Storage Architecture).

A highly available storage architecture lets you:

• Store and access information on an as-needed basis.
• Extend your resources through virtual capabilities.
• Scale up and scale out to meet changing needs.
• Simplify storage management.
• Protect your data and your investment
• Improve efficiency of storage systems by helping you manage more storage with the same resources.

Careful selection of the type of storage system is another important consideration. For this there are three technical architectures like DAS, NAS, and SAN.

TECHNICAL ARCHITECTURES
DAS (Direct Attached Storage) is commonly used for storing data. But it is limited because it does not allow an organization to share data easily. It is not an enterprise network storage architecture in a true sense. It is also inflexible and has short-term cost and technology benefits. NAS (Network Attached Storage) and SAN (Storage Area Network) have evolved as more reliable enterprise network storage architectures. Let's look at all three of them in detail.

DAS is the most common form of storage used by companies. Most computer storage devices like disk drives or JBODs (Just a Bunch of Disks), tape devices, and RAID systems are directly attached to a client computer. They use various adapters and standardized software protocols like SCSI (Small Computer Systems Interface) and FC (Fiber Channel).

In DAS, I/O (Input/Output) is done in blocks from the server to the storage. This type of attachment has set the standard for performance and utilization by the server. With DAS, performance is typically characterized by response time for access to data and by bandwidth for aggregate transfer rate of data.

DAS has limited flexibility and does not allow you to scale outward easily. A company's network will typically continue to grow while data on the various DASs will remain scattered at different locations of the network. This will not allow all the users in the network to access and share the data. Management becomes a hellish task with so many disparate 'islands' of information all over. Data security and protection is equally difficult as no form of centralized control can be established.

It's no secret that companies that are serious about data storage cannot rely solely on DAS, as an effective storage strategy—it has too many limitations. IDC estimates that storage management costs can be reduced by 40 percent and IT administrators can manage 750 percent more storage capacity by moving out of the traditional DAS.

However in a SOHO (Small Office Home Office) environment with very few users, a DAS can handle the storage needs fairly well.

NAS is a specialized file server that can be plugged into the network (LAN) just like a network printer, hence the name 'network-attached'. It provides file-level access to data and uses standardized protocols like NFS (Network File System-Unix-based), CIFS (Common Internet File System-Windows-based), and TCP/IP to communicate. One of the attractive features of a NAS is that it can serve both Unix and Windows users seamlessly and share the same data between the different architectures. It is ideal for mid-sized and not-so-large companies who have a fairly large volume of data.

With a NAS, storage does not become an integral part of the server. It has a storage-centric design where the server still handles all the processing of data but the NAS device delivers the data to the user. If you have an overflowing hard disk on your main server, a NAS device can allow you to stretch and offer breathing room. You can move archives or completed projects from the main server to the NAS and still allow users in the network to access it. Data storage, security, and backup management can also be centralized.

Computer systems can access data from a NAS over a network via a file 'redirector' that changes the access to a file from the native file system (on the originating computer system) to a network operation using TCP. The remote NAS device runs software that allows the file system to support an individual client access. The file system on the NAS server determines the location of the data requested by the application client whether it is in its cache or on the storage.

NAS causes overhead for using the LAN since it rides on the TCP/IP protocol stack and consumes processing power. It may bring latency into the network when another processing element is placed in the I/O access path.

STORAGE AREA NETWORKS
A SAN is a high-speed dedicated storage network or subnetwork, which can integrate RAID arrays, tape backups, CD-ROM libraries, and JBODs. The SAN network allows data transfers between computers and disks at the same high peripheral channel speed, as if it is directly attached. It is ideal for large companies that have networks across large geographical areas and medium companies who expect quick growth. SANs are used by industries like petroleum, banks and financial institutions, and retail manufacturing.

SAN deployments are largely driven by the use of the FC (fiber channel) standard as a common interface. FC makes use of a circuit/packet switched topology capable of providing multiple simultaneous point-to-point connections between devices. It offers advantages like good connectivity and scalability, and allows large distances. The SAN advent is driven by new requirements of applications like data warehousing, data mining, and OLTP (On Line Transaction Processing), which need high bandwidth and tolerate zero latency. The FC interconnection protocol allows data transmission speeds up to 1 Gbps, which is much faster than traditional SCSI-based PC and server devices which have a maximum speed of 160 Mbps.

SANs see storage as separate from a server like NAS. But unlike NAS, the SAN architecture involves an independent network or subnetwork. It provides its own network to storage and offloads primary network from all storage related I/O and backups. With a SAN, servers are not directly involved in the storage process. They simply monitor it. And by removing I/O from the servers and the LAN/WAN, you free up bandwidth for applications. This allows enhanced network performance and removes traditional bottlenecks. With the use of a SAN switch you can permit concurrent traffic between all servers of the network and share all the storage devices.

SANs support disk mirroring, backup and restore, archival and retrieval of archived data, data migration from one storage device to another, and sharing of data among different servers in a network. SANs can incorporate subnetworks with NAS systems.

FC is, without any question, the backbone of a SAN architecture but SCSI can be used as the interface to link storage devices to the SAN backbone. This is because FC supports simultaneous transfer of different protocols. SANs also support ESCON (IBM's optical fiber interface).

Instead of putting the storage directly on the network, the SAN concept puts a network in between the storage subsystems and the server. This means that a SAN actually adds network latency to the DAS storage model. SAN standards are still in the formative stage and vendors like EMC, Compaq, and HP have announced proprietary standards. This collection of proprietary architectures may create roadblocks to successful NAS and SAN integration and data sharing between heterogeneous platforms.