Technology recently acquired from String Bean Software will take the upcoming R2 version of Windows Storage Server 2003 beyond its predecessor's role as a network attached storage (NAS) device. The technology, called WinTarget, allows other servers to connect to Windows Storage Server 2003-based storage over a storage area network (SAN) rather than with file-sharing protocols. This is important because many applications work poorly or not at all when accessing networked storage using file-sharing protocols, a limitation that keeps some customers from considering Windows Storage Server 2003 appliances to meet all of their data storage needs.

What Is WinTarget?

SANs enable servers to access one or more external, shared disk-storage arrays over a network protocol designed for transferring block-level disk data; for Windows and Unix/Linux servers this protocol is either Fibre Channel or Internet Small Computer System Interface (iSCSI). Traditionally, these storage devices do not run a general purpose OS, such as Windows or Linux, but instead run a small hardware-specific OS tailored for their primary task of reading and writing block-level data to disk.

Unlike the more mature Fibre Channel protocols used in most SANs today, iSCSI traffic does not require special switches or routers, which makes it useful for both local and remote storage access. Servers use iSCSI initiator software to send disk input/output (I/O) commands over TCP/IP networks to storage devices running iSCSI target software.

Microsoft already ships an iSCSI initiator for Windows Server 2003 that allows it to connect to iSCSI storage arrays that come with their own target software, but String Bean's WinTarget product is iSCSI target software for Windows OSs, thereby allowing a Windows computer to function as an iSCSI storage array and provide block-level storage to other servers on the SAN.

Microsoft intends to offer the WinTarget technology in its upcoming release of Windows Storage Server 2003 R2, due out in the second quarter of 2006. Windows Storage Server is an edition of Windows Server 2003 specialized for NAS devices, which are scalable, high-availability file servers with additional features to simplify backup, reorganization of disk space, and other management tasks. The Windows Storage Server edition is only available preinstalled and preconfigured on NAS appliance hardware available from OEMs, which include major names such as Dell, EMC, Hewlett-Packard, and IBM.

Unlike String Bean, Microsoft has no plans to offer WinTarget for Windows Server 2003 or Windows XP.

Why Hybrid SAN/NAS Devices?

NAS servers give other servers or workstations network access to pools of disk storage—whether connected directly (direct attached storage, or DAS) to the NAS server or connected to the NAS server via a SAN to a storage array—using a network file-sharing protocol, such as the Server Message Block (SMB) protocol or the Network File System (NFS) protocol. However, the NAS approach does not work well for certain types of applications, primarily database management systems, which are designed and optimized to read and write data at the block level rather than the file level. For example, Microsoft does not recommend using NAS-based storage with SQL Server and will support it only on NAS hardware that meets certain requirements; even then, Microsoft includes disclaimers stating that database performance will be severely degraded. Similarly, using NAS with Exchange 2003 is supported only under certain conditions and will yield suboptimal performance compared with SAN or DAS storage.

Microsoft claims that more customers will be interested in Windows Storage Server systems if the appliances can also provide storage access to application servers over the iSCSI block-level storage protocol. The option to include WinTarget technology in Windows Storage Server 2003 R2 will allow OEMs to offer hybrid devices that support both file- and block-level storage access over a TCP/IP network. However, Microsoft cautions that the overhead of the Windows OS and the general-purpose server hardware used by Windows Storage Server appliances will prevent them from matching the raw disk I/O performance of dedicated (and more expensive and complicated) iSCSI SAN storage arrays.

Resources

Microsoft's support for SANs and networked storage is described in "Driving Down the Cost of SANs" on page 3 of the May 2005 Update and at www.microsoft.com/windowsserversystem/storage.

Windows Storage Server is described in "Windows Server 2003 Drives New Storage Server" on page 10 of the July 2003 Update and at www.microsoft.com/windowsserversystem/wss2003.