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Tip: Know the Right Way to Resynchronize and Repair a Mirrored Set


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Windows Server 2008 R2 automatically synchronizes mirrored volumes on dynamic drives. However, data on mirrored drives can become out of sync. For example, if one of the drives goes offline, data is written only to the drive that’s online. You can resynchronize and repair mirrored sets, but you must rebuild the set using disks with the same partition style—either master boot record (MBR) or GUID partition table (GPT). You need to get both drives in the mirrored set online. The mirrored set’s status should read Failed Redundancy. The corrective action you take depends on the failed volume’s status:
  • If the status is Missing or Offline, be sure that the drive has power and is connected properly. Then start Disk Management, right-click the failed volume, and click 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 click Resynchronize Mirror.
  • If the status is Online (Errors), right-click the failed volume, and then click 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 click Resynchronize Mirror.
  • If one of the drives shows a status of Unreadable, you might need to rescan the drives on the system by choosing Rescan Disks from Disk Management’s Action menu. If the drive status doesn’t change, you might need to reboot the computer.
  • If one of the drives still won’t come back online, right-click the failed volume, and then click Remove Mirror. Next, right-click the remaining volume in the original mirror, and then click Add Mirror. You now need to mirror the volume on an unallocated area of free space. If you don’t have free space, you need to create space by deleting other volumes or replacing the failed drive.


From the Microsoft Press book Windows Server 2008 Administrator’s Pocket Consultant, Second Edition by William R. Stanek.

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