Windows 7 / Getting Started

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Breaking or Removing a Mirrored Set

Windows Server 2008 provides two ways to stop mirroring. You can break a mirrored set, creating two separate but identical volumes. Or you can remove a mirror, which deletes all the data on the removed mirror.

To break a mirrored set, follow these steps:

1. In Disk Management, right-click one of the volumes in the mirrored set, and then choose Break Mirrored Volume.
2. Confirm that you want to break the mirrored set by clicking Yes. If the volume is currently in use, you'll see another warning dialog box. Confirm that it's okay to continue by clicking Yes.
   Windows Server 2008 will then break the mirrored set, creating two independent volumes.

To remove a mirror, follow these steps:

1. In Disk Management, right-click one of the volumes in the mirrored set, and then choose Remove Mirror. This displays the Remove Mirror dialog box.
2. In the Remove Mirror dialog box, select the disk from which to remove the mirror. If the mirror contains a boot or system volume, you should remove the mirror from the secondary drive rather than the primary. For example, if Drive 0 and Drive 1 are mirrored, remove Drive 1 rather than Drive 0.
3. Confirm the action when prompted. All data on the removed mirror is deleted.

Resolving Problems with Mirrored Sets

Occasionally, data on mirrored volumes can get out of sync. Typically, this happens if one of the drives in the set goes offline or experiences temporary I/O problems and, as a result, data can be written only to the drive that's online. To reestablish mirroring, you must get both drives online and then resynchronize the mirror, but you should rebuild the set using disks with the same partition style-either MBR or GPT. The corrective action you take depends on the drive status.

Note: When mirroring boot volumes, Windows requires you to use the same partition style. With data volumes, you can mirror between GPT and MBR.

The Missing or Offline status usually happens if drives have been disconnected or powered off. If the drives are part of an external storage device, check the storage device to ensure that it is connected properly and has power. Reconnecting the storage device or turning on the power should make it so the drives can be accessed. You then must start Disk Management and rescan the missing drive by selecting Rescan Disks on the Action menu. When Disk Management finishes, right-click the drive, and choose Reactivate Volume. The drive status should change to Regenerating and then to Healthy. If the volume doesn't return to the Healthy status, right-click the volume, and then choose Resynchronize Mirror.

A status of Failed, Online (Errors), or Unreadable indicates I/O problems with the drive. As before, try rescanning the drive, and then try to reactivate the drive. The drive status should change to Regenerating and then to Healthy. If the volume doesn't return to the Healthy status, right-click the volume, and then choose Resynchronize Mirror.

If these actions don't work, you must remove the failed mirror, replace the bad drive, and then rebuild the mirror. To do this, follow these steps:

1. Right-click the failed volume, and then select Remove Mirror.
2. You now must mirror the volume on an Unallocated area of free space on a different disk. If you don't have free space, you must create space by shrinking a volume, deleting other volumes, or replacing the failed drive.
3. When you are ready to continue, right-click the remaining volume in the original mirror, and then select Add Mirror. This displays the Add Mirror dialog box.
4. Use the Disks list to select a location for the mirror, and then click Add Mirror. Windows Server 2008 begins the mirror creation process, and you'll see a status of Resynching on both volumes.