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Everything You Wanted to Know About Windows' Storage Capabilities
Learn what storage features have appeared and will appear in the major releases of the Windows Server operating system.
by Dilip C. Naik

Posted November 21, 2003

About This Article:
This article is adapted from Inside Windows Storage: Server Storage Technologies for Windows 2000, Windows Server 2003 and Beyond by Dilip C. Naik. Copyright 2003 by Addison-Wesley. Reproduced by permission. All rights reserved.

Many storage professionals fancy their knowledge to be complete with respect to storage technology, but they are looking for details of storage features that have appeared or will appear with particular releases of the Windows Server operating system. I will attempt to describe storage features in the post-NT Windows cycle, but the Microsoft release process can sometimes make the discussion confusing.

For future versions of Windows, assume in this article that features discussed by Microsoft will ship. But note that there is no guarantee that they will ship, let alone when and whether the functionality and architecture will be as described here. The reader should take all of this into account before making any decisions.

Windows 2000
The most remarkable advance of Windows 2000 was to make the Windows NT platform highly conducive to being used in a SAN or NAS environment. This release also established Windows as a player in the NAS environment. There is a long list of storage-related advances made in Windows 2000.

Improved Storage Unit Accessibility. Windows 2000 dramatically enhances storage unit accessibility by vastly reducing the scenarios in which a system reboot is required to change storage unit configurations (for example, add, remove, grow, or shrink volumes), and by vastly increasing the number of storage units that the operating system can handle.

Windows NT 4.0 requires that a system be rebooted before it can access a new physical storage device (called a target). Windows 2000 plug-and-play (PnP) improvements support the dynamic addition and removal of storage targets.

New Volume and Disk Management. Windows 2000 introduced dynamic disks, a logical concept that is applied to the physical disk. Physical disks remain basic disks with a partition table, just as they were in Windows NT 4.0, until they are explicitly converted to dynamic disks. This new partition table is stored in a redundant fashion, to ensure that it is always available, even when some disk clusters are corrupted.

Dynamic disks can be recognized only by Windows 2000 and later versions of Windows NT. Dynamic disks still retain the old-style partition table as well, to ensure that data does not become corrupted when the disk is accidentally referenced either by a Windows NT 4.0 system or in a heterogeneous operating environment in which the other operating system understands only the old-style partition table. However, the partition table simply contains a single entry that shows the whole disk as being in use. This old-style partition table does not reflect the true logical organization of the disk.

There are two new kernel mode components. The Mount Manager handles mount operations for basic and dynamic disks, including assigning drive letters. The Partition Manager handles PnP operations, as well as power management and Windows Management Instrumentation (WMI) operations on disk partitions. The two combine to provide functionality that allows two volume managers to coexist in the system. One is the old FtDisk driver, which in some senses is indeed a volume manager. The other one is either the default Logical Disk Manager (LDM) shipped with Windows 2000 or the Logical Volume Manager (LVM) upgrade product sold by VERITAS.

Together with improvements in PnP, the new disk management features ensure the following:

• Volumes may be dynamically shrunk and grown without the operating system having to be shut down and the system rebooted.
• Volumes may be mounted and unmounted on the fly.
• Volumes may be converted from using one RAID class to using another RAID class without a system reboot.
• Legacy volumes, including volumes that use a form of RAID supported by the legacy FtDisk volume manager, are still supported.
• Dynamic disks are self-describing; that is, all metadata needed to figure out the layout of a disk is stored on the disk itself.
• The new disk management features make a GUI and command-line tool available for disk management.
• New APIs have been added to enable volume management applications.