The French word for "without" is sans—an appropriate word to use if you're talking about Windows environments and Storage Area Networks (SANs). The groundswell of SAN deployments in the IT industry has only recently begun to reach the Windows world. Let's look at why SAN adoption has been slow in the Windows environment and why SANs are an important technology that every Windows administrator can leverage.

Content with the Status Quo?
Strategic Research ( estimates that between 1996 and 1998, data stored on worldwide Windows NT­based systems grew from 11PB to 39PB and by the end of 2002 will grow to more than 260PB. Despite this rapid data growth, Direct Attached Storage (DAS) remains the mainstay in the Windows environment. Most Windows administrators have been content with the simple and straightforward configuration and management, excellent performance, and low cost that DAS provides. Storage vendors haven't helped much. Most enterprise-class storage vendors, such as EMC, Hewlett-Packard (HP), Hitachi, and IBM, have been slow to recognize the Windows storage market; they've been content to revel in their huge installed base in mainframe and midrange environments. However, many of these vendors are beginning to realize that Windows represents the largest growth area in the storage business.

Microsoft has been equally slow in embracing new storage technologies. Not long ago, if you talked to Microsoft about deploying Windows, Microsoft Exchange Server, or Microsoft SQL Server on a SAN or Network Attached Storage (NAS) device, you'd get that "deer in the headlights" look. In Microsoft's defense, the company must ensure supportability of its products, and the investment of capital, process, and personnel to test its products with SAN and NAS is substantial. But Microsoft has made the necessary investments to position the company to maximize the value that technologies such as SAN bring to the Windows environment. Windows .NET Server (Win.NET Server) includes features such as multipath I/O (MPIO), Host Bus Adapter API (HBA API), Volume ShadowCopy Service (VSS), and support for booting the OS from a SAN. These important features, plus enhancements in other areas (e.g., a completely redesigned storage driver and port model in Win.NET Server), will finally let the Windows OS take full advantage of the new storage technologies.

Two factors that have caused Windows administrators to lag behind in SAN implementation are cost and complexity. First, until recently, IT has linked storage investment decisions to the purchase of an individual server, making the cost easily justifiable based on the application or service that the server will provide. DAS requires no more infrastructure than power cords and SCSI cabling, which add relatively little complexity to the environment. SANs, however, require a substantial investment in infrastructure and personnel. SANs rely on a full-blown Fibre Channel infrastructure complete with hubs, expensive switches, and costly fiber cabling.

Second, SAN technology requires a significant learning curve for existing personnel or a substantial investment in additional personnel who have SAN experience. Implementing a SAN affects storage design, capacity planning, provisioning, and disaster recovery. Consequently, implementation provides a substantial barrier to entry for smaller organizations, and in many cases, only large enterprises with large budgets and on-staff expertise can make the jump to SANs in the Windows environment.

What Do SANs Offer?
Until now, Windows administrators haven't been sufficiently motivated to move en masse to SANs. However, storage-data growth in every environment, including Windows, has left administrators, system designers, and IT managers scrambling for technologies that can quench their thirst for data scalability, availability, reliability, manageability, and lower total cost of ownership (TCO). Many enterprises have reached the limits of DAS, but SANs fulfill all these needs.

Scalability. SANs shine when it comes to capacity scalability. Although using DAS to build a 300GB server is rather easy and inexpensive, using DAS to build a 4TB or 5TB server isn't palatable. By letting designers build disk units on the SAN controller to present to the OS as LUNs, SANs make such a task much more feasible. System designers who use SAN technology can plan for systems that have multiple terabytes of storage and still leave plenty of room for growth.

Scaling large amounts of storage also requires that you maintain adequate levels of performance for that storage. A misconception among many users is that SANs provide better performance than DAS does. Although the SAN interconnect (100MBps to 2GBps) is inherently faster than SCSI bus speeds (40MBps to 80MBps), anyone who has been around most business applications in the Windows environment (e.g., SQL Server, Exchange Server) knows that what matters is I/Os per second, not megabytes per second.

Inherently, SANs don't necessarily deliver more I/Os per second for a given LUN than DAS does. However, SANs do deliver an infrastructure based on Fibre Channel, which provides a fabric that can support a greater degree of scalability than traditional DAS implementations based on SCSI buses. In terms of general I/O performance, most users find that SANs deliver levels of performance that are equivalent to those of DAS. However, designing for greater I/O performance involves increasing the number of disk devices available in a given unit. In general, most SAN implementations provide a greater degree of disk-per-LUN scalability than DAS does. Although SAN technology doesn't provide any raw performance advantages over DAS, it provides a way to scale I/O performance while scaling capacity.

Availability and reliability. SANs also provide technologies that enhance system and data availability and reliability. Many of these technologies aren't new to SANs but are widely implemented as standard SAN features.

Volume or LUN cloning and snapshots are examples of key availability technologies. Implemented at the controller level, these features create redundant data volumes for recovery use in Windows servers and applications such as Exchange and SQL Server. Clones are completely redundant copies of data, whereas snapshots are point-in-time block mappings of data volumes. (Snapshots aren't completely redundant data sets but a combination of changed and unchanged data blocks within a storage pool.)

Neither Windows 2000 nor Exchange offer native support for snapshot or clone technology, but Win.NET Server will feature VSS, which provides native OS support for clone and snapshot technologies. Hardware and software vendors of snapshot and clone technology products will be able to develop VSS providers to plug their products into the VSS framework. Applications will use the VSS services through writers, which implement application-specific recovery packages.

Other interesting availability and reliability technologies available with SANs include Remote Data Replication (essentially, remote cloning) and SAN-attached backup (the ability to attach a backup server directly to the SAN rather than to the LAN or server attachment). The number of rapid-recovery solutions and capabilities that vendors can build with SAN technologies in the Windows environment are endless and are exactly what Windows administrators are clamoring for to increase system and data availability.

Manageability and lower TCO. Managing individual servers with individual storage systems is fairly simple as long as the number of servers is small. However, as the number of servers and the amount of data housed on these servers grow, IT departments wonder how they will manage the systems.

IT is turning to SAN technologies to simplify storage management and to aid in consolidation efforts. With features such as Selective Storage Presentation (SSP) and virtualization, administrators can leverage SANs to bring their data under centralized control and management. Selective storage presentation and virtualization provide a secure and manageable view of the physical storage abstracted into solution-specific storage units. These SAN features also facilitate data and storage provisioning and general Storage Resource Management (SRM).

Enterprise storage facilities will move from disparate systems owned by OSs and applications to an enterprise pool of storage that users can dynamically provision based on user and application requirements—a huge benefit to server and service consolidation projects that must aggregate large amounts of data and storage for one large server or application. Further advancements in SRM and new technologies such as the SCSI over IP (iSCSI) protocol will advance SANs' ability to provide increased manageability and lower the TCO for SAN deployment and operation in both large and small enterprises.

Windows administrators need the benefits of SAN and NAS storage technologies. With these technologies' advances and proliferation, the costs and barriers to deployment should eventually disappear. Microsoft is also embracing these technologies on the Windows platform (particularly in Win.NET Server) and in .NET Enterprise Server products such as Exchange and SQL Server. It's time for Windows IT departments to enjoy the benefits of Windows with SANs—or as the French would say, "Windows avec SANs."