Spanned volumes. Microsoft renamed NT's volume sets spanned volumes in Win2K. Despite the name change, the underlying concept remains the same—spanned volumes contain disk space from two or more physical disks. You can use Win2K's Logical Disk Manager (LDM) to extend an existing simple volume into a spanned volume by adding disk space from other disks on the system. The LDM, which Screen 1 shows, is Win2K's Microsoft Management Console (MMC)-based disk-management snap-in and the successor to NT 4.0's Disk Administrator utility.
Win2K and NT partitions, volumes, and sets can be confusing. To clarify, in NT parlance, disks contain partitions, which are basic disks' primary unit of division. Win2K refers to partitions as volumes. In both OSs, each partition or volume must be a particular type (e.g., primary, extended, simple, spanned, volume set, mirror set). Table 1 compares Win2K and NT disk terminology.
Which file system (e.g., NTFS, FAT, FAT32) you use to format a volume or partition is an entirely separate matter. For the most part, Win2K and NT offer more than one file system choice for a given volume type. Three notable exceptions are volume sets, spanned volumes, and simple volumes that you want to extend using additional free space on the same drive, all of which you must format as NTFS. However, simple volumes can be FAT or FAT32 if they use only one area of free space on one drive.
Dynamic Disk Enhancements
Dynamic disks support new features and technology that provide enhanced fault tolerance and online-management capabilities for disk volumes. These enhancements result in higher availability for Win2K servers than basic disks provide for NT servers.
Unlike basic disks, dynamic disks maintain information about critical disk data structures in multiple locations. In addition, dynamic disks don't rely on one partition table for volume type and location information. Instead, all dynamic disks maintain a 1MB database at the end of the drive that contains not only crucial information about the volumes on that dynamic disk but also information about all dynamic disks on the system. This database contains information similar to information that a basic disk's partition contains, including the starting and ending sectors, total number of sectors, and the volume or RAID type of each dynamic disk volume. (This database doesn't include the FAT data for FAT and FAT32 volumes or the Master File Table—MFT—data for NTFS volumes; the system maintains this information separately.) The database contains information for all volumes, and the system duplicates the database on all dynamic disks. This functionality greatly increases the possibility of recovering the system in the event of database damage.
Win2K automatically establishes and replicates the database without user intervention. In addition, the system can automatically use the database's information to recover a corrupted or destroyed volume database. Corruption or destruction of a basic disk's partition table under NT 4.0 is a catastrophic event, but Win2K can automatically repair this type of condition on a dynamic disk without the user even knowing what happened. In the event of database corruption, Win2K simply identifies a dynamic member disk with a complete undamaged copy of the database, then copies the undamaged database version to the corrupted disk.
Win2K introduces a new concept called disk groups, which are what the name implies: groups of dynamic disks. Win2K automatically creates a disk group as you add dynamic disks to your system. Dynamic disks replicate the volume database with the members of their disk group. By default, Win2K permits only one disk group. The system derives the disk group's name from the computer name and adds a Dg0 suffix. If you're curious about the name of your system's disk group, check the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSetServices\dmio\Boot Info\Primary Disk Group\Name Registry subkey. Win2K's LDM is a light version of VERITAS Software's Logical Disk Manager Pro, and if you use the Pro version of VERITAS' product, you can create and manage multiple disk groups in Win2K.
Another benefit of Win2K's dynamic disks is that you can manage disks online without rebooting the system. Unlike basic disks' reconfiguration options (e.g., creating, extending, and mirroring a volume), which require a system reboot to take effect, dynamic disks let you change volume configurations on the fly. Win2K also lets you add new dynamic disks to the system (e.g., with buses that support hot-pluggable drives) without rebooting. Unlike NT 4.0's Disk Administrator, almost all disk-configuration changes you make in Win2K's LDM take effect immediately—you don't need to select a separate menu command to save or commit changes you make during a session. These new storage-management features are a quantum improvement over those in NT 4.0.
Dynamic Upgrades
You can use three methods to create a dynamic disk: convert an existing basic disk, import an existing dynamic disk set from another Win2K system, or configure a new, uninitialized drive as a dynamic disk. You use the conversion method when you're upgrading an existing NT machine to Win2K or migrating legacy disks to a Win2K system. You create and convert dynamic disks from the LDM.
Converting basic disks to dynamic disks isn't mandatory. Win2K can work with basic disks as well as dynamic disks, and a Win2K system can contain combinations of basic and dynamic disks. The first time you run the LDM on a system that contains one or more basic disks, Win2K will ask whether you want to convert the basic disks to dynamic disks. If you forgo conversion, you can convert later by right-clicking a basic disk's drive in the left pane of the LDM console and selecting Upgrade to Dynamic Disk, as Screen 2 shows. This option isn't available if you're using a laptop computer because Microsoft doesn't support dynamic disks on laptops.
Dynamic Disk Dilemmas
Unfortunately, several situations exist in which Microsoft doesn't recommend using dynamic disks because they're not beneficial or they just don't work. One limitation is that Win2K is the only OS that can use and read dynamic disks and their volumes, even if you format the volumes with a file system that other OSs support (e.g., FAT or FAT32). If you're running a multiboot system, you need to be aware of this restraint before you convert your basic disks.
In addition, removable drives such as Zip, Jaz, SyQuest, and magneto-optic drives and hard disks that use USB or IEEE 1394 connections don't support dynamic disks. In the article "IEEE 1394 Hard Disk Support in Windows 2000" (http://support.microsoft.com/support/
kb/articles/q244/9/19.asp), Microsoft states that the reason for this lack of support is the hot-removable nature of removable drives. Removing a drive that contains a dynamic disk from one of these systems invalidates the contents of the dynamic disks' replicated volume database.
The fact that you can't use dynamic disks on laptop computers can also be a problem. I suspect that this lack of support relates to the fact that you can remove and swap many laptops' hard disks. As with removable drive types, removing dynamic disks causes problems with other dynamic disks on the system. However, dynamic disks don't provide any major advantages to laptop users. A dynamic disk's replicated volume database is useful only on systems that contain multiple physical drives, which is rarely the case for laptops. In addition, many Win2K laptops are multiboot systems that also run Win9x, DOS, Linux, BeOS, or other OSs, and dynamic disks and their volumes are unreadable to any OS other than Win2K.
Dynamic disk volumes support the same RAID levels as basic disk partitions (i.e., 0, 1, and 5). Although you can import and maintain basic disks' existing RAID volumes in Win2K, you can't create new RAID volumes on basic disks—Win2K supports the creation of new RAID volumes only on dynamic disks. If you need to add RAID volumes to your Win2K system, you must either add a new disk and define it as dynamic or convert an existing basic disk that contains enough free space for the new RAID volume.
Be aware that you can't easily convert a dynamic disk and its volumes back to a basic disk. The only way to accomplish this task is to remove each volume from the dynamic volume, at which point you can convert the disk back to a basic disk. To preserve the data on the dynamic disk's volumes, you must back up and restore the files on those volumes.
Finally, Win2K doesn't let you extend a simple volume on a converted dynamic disk by adding free space to the disk or convert a simple volume on a converted dynamic disk to a spanned volume by adding free space on a different disk. The reason for this limitation is that basic disk partitions that you convert to simple volumes on dynamic disks must retain their partition table entries in the MBR so that Win2K can boot from the volume or install to it. (Win2K Setup lets you perform installations only to dynamic disks that include the system or boot volume.) Expanding the simple volume would disable the ability to boot from or install to the volume.
Deliberating Disk Decisions
Dynamic disks are a core technology in Win2K and represent a significant step in the evolution of OS storage management. However, in certain environments dynamic disks present limitations, including backward-compatibility problems with legacy OSs and lack of support from some hardware configurations and devices. Understanding how dynamic disks differ from their basic disk predecessors and knowing dynamic disks' strengths and weaknesses will help you make the best disk-configuration choices for your Win2K systems.