Dynamic Disks and Disk Groups

Windows 2000 uses a new disk layout that extends beyond disk partitioning. New to Windows 2000 are dynamic disks and Disk Groups. Dynamic disks allow more flexibility during configuration than basic disks. For example, dynamic disks allow you to increase the size of a volume or add a mirrored volume without restarting the computer. A Disk Group is a collection of disks managed as a collection that helps you organize dynamic disks and helps prevent data loss.

Disk Groups are unique to dynamic disks. Each disk in a Disk Group stores replicas of the same configuration data. This configuration data is stored in a 1-megabyte (MB) region at the end of each dynamic disk. Since this information is contained on each disk, you can move them to another computer or install another disk without losing this information. All dynamic disks in a computer are members of the same Disk Group and have the following characteristics:

• They overcome partitioning rules from Windows NT 4.0.
• They extend or create fault-tolerant sets without the need to restart the computer.
• They are not registry dependent: that is, disk information for both basic and dynamic disks and fault tolerance information for dynamic disks is kept on the disk in Windows 2000.

Note

To simplify use with docking stations, you cannot use dynamic disks on portable computers. Also, you cannot use dynamic disks on removable media. This simplifies movement of media between machines.

Converting Basic Disks to Dynamic Disks

In Windows 2000, you can convert a basic disk to a dynamic disk. When you convert a disk, any existing partitions or fault tolerance structures on the disk are checked and then the disk is assigned a Disk Group identity and a copy of the current Disk Group configuration. Windows 2000 also adds dynamic volumes to the configuration.

Note

By default, when you add a disk to an existing computer, it is considered a new disk. New disks are always dynamic disks.

Moving Disks

You can move basic and dynamic disks from one computer to another. For both basic and dynamic disks, you need to physically move the disk from the computer, and then either restart the computer or use the Rescan Disks command on the Action menu of Disk Management.

When you remove a dynamic disk from a computer, the remaining online dynamic disks retain information about it and its volumes. The removed disk is displayed in Disk Management as a Dynamic/Offline disk and assigned the status of "Missing."

You need at least one online dynamic disk to retain information about Missing disks and their volumes. When you remove the last dynamic disk, you lose the information, and the Missing disks are no longer displayed in Disk Management.

Note

When you move basic fault-tolerant sets from a computer running Windows NT 4.0, you need to save the configuration to a floppy disk, and then use Disk Management to restore the hard disk configuration. It is strongly recommended that you move all disks from the fault-tolerant set.

Connecting New Disks to a Computer

After you connect the disks to the new computer, from the Disk Management snap-in, select Rescan Disks on the Action menu. The New Signature Wizard is displayed. When you physically connect a dynamic disk, the rescan causes the disk to be displayed in Disk Management as Dynamic/Foreign. You might need to convert it to Dynamic/Online, and then activate the volumes. When you connect a new disk to a computer, or rescan the dynamic mirrored volume and move only one disk, it displays as Dynamic/Offline, and you need to manually activate it.

Note

When you connect a basic disk with existing partitions, you must select Rescan Disks from the Disk Management snap-in.

Importing Foreign Disks

If you move one or more disks from a Disk Group to another computer that contains its own Disk Group, the Disk Group you moved is marked as Foreign until you import it into the existing group.

To use Foreign/Dynamic disks, use the Import Foreign Disks operation associated with one of the disks. The manual operation lists one or more Disk Groups, identified by the name of the computer where they were created. If you expand the details on a Disk Group, it lists the locally-connected disks that are members. Click the appropriate Disk Group, and then click OK. You can then view the dialog box that lists volumes that were found in the Disk Group, along with some indication of the status of those volumes.

Since volumes can span multiple disks using simple disk spanning, striping, mirroring, or RAID-5 redundancy mechanisms, the display status of a volume in the Import Foreign Disks dialog box can become complicated if not all of the disks have been moved. Another complication can arise from moving a disk, and then later moving additional disks. This is supported, but can be complicated. For this reason, all fault tolerant and non-fault-tolerant volumes that span disks should be moved at the same time.

The state of a volume after import depends on whether the volume is simple, mirrored, RAID-5, or spans multiple disks (simple striping behaves like spanning in this respect). It also depends on if the whole or part of the volume is moved, and if the volume is moved incrementally. The state depends on whether changes to the configuration of a partially moved volume were made on the original or the new computer:

• When all disks that contain parts of a volume are concurrently moved from one computer to another, the state of the volume after the import is identical to the original state. All simple volumes on any moved disks are recovered to their original state.
• On a non-redundant volume that spans multiple disks, if only some disks are moved from one system to another, the volume is disabled during import: it also becomes disabled on the original system. As long as the volume is not deleted on either the original or the target system, the remaining disks can be moved later. When all disks are finally moved over, the volume is recovered to its original state.
• RAID-5 volumes can remain online if they are missing one disk. The status of the volume is displayed as either Failed Redundancy or Failed Redundancy (At Risk). If a disk is moved to a different computer, all or all but one of the disks must be moved. If all disks are moved, the status of the volume cycles from Regenerating to Healthy. If all but one of the disks are moved, the status of the volume is Failed Redundancy (At Risk). Whether the volume remains online depends on whether the data is known to be valid or can be regenerated from the parity and the data. Parity starts out as invalid when a RAID-5 volume is first created, since the parity blocks must be computed, which takes time. Parity is also marked as invalid after a system crash, because an in-progress write can leave a discrepancy between parity blocks and the corresponding data blocks. If the parity of a RAID-5 volume is valid, one disk can be missing and the RAID-5 volume still becomes (or remains) online. If parity is not valid, then all parts of the RAID-5 volume need to be available for the volume to become (or remain) online.
• If both halves of a mirrored volume are moved as a set, the volume functions normally and your data continues to be fault tolerant. If only one half of a mirrored volume is moved to another computer, and then you return it to the original computer, the two halves of the original mirrored volume do not function as a mirrored volume. To restore the mirrored volume, break the original mirrored volume and then recreate it.
• If one up-to-date mirror is moved first, the mirror on the resulting Missing disk (for the non-moved mirror) can be removed and reallocated to another disk. This leaves a fully mirrored volume on the target computer. In this case, if the second original mirror is moved over, it conflicts in a way that cannot be resolved readily. When this happens, the second mirror comes over as a new volume.

Warning

Note that when removing and moving disks with mirrored volumes, if one of the volumes becomes damaged during the move, your data is no longer fault tolerant.

It is better to remove all disks at the same time, and to add all disks at the same time. With SCSI disks, this is fairly easy: stop using the disks, and then defer the Rescan disks request until all disks are removed.

With any kind of disk, turn off the original system before removing the disks, and then turn off the target system before adding the disks.

For information about disk groups, see the Knowledge Base link on the Web Resources page at http://windows.microsoft.com/windows2000/reskit/webresources.

Simple Volumes

Simple volumes are the dynamic disk equivalent of primary partitions in Windows NT 4.0 and earlier versions. When you have only one dynamic disk, you can only create a simple volume. Simple volumes can be created on dynamic disks only. They cannot contain partitions or logical drives, and they can only be accessed by Windows 2000.

You can increase the size a simple volume to include unallocated space on the disk, but the volume must be formatted with the version of NTFS used in Windows 2000. You cannot increase the size of a simple volume that was converted from a basic disk partition. Increasing the size of a simple volume to include space on other disks of the same computer creates a spanned volume.

Spanned Volumes

Spanned volumes are created from unallocated space from between two and 32 dynamic disks. The areas of unallocated space used to create spanned volumes can be of different sizes. You can increase the size of a spanned volume, but the volume must be formatted with NTFS.

After a spanned volume is extended, no portion of it can be deleted without deleting the entire spanned volume. Spanned volumes cannot be mirrored or striped and do not offer fault tolerance. If one of the disks containing a spanned volume fails, the entire volume fails.

Note

Only Windows 2000 can recognize a spanned volume. On a multiple-boot computer, spanned volumes are unusable by other operating systems.

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