Mirrored Volumes
Mirrored Volumes
A mirrored volume uses volumes stored on two separate physical disks to “mirror” (write) the data onto both disks simultaneously and redundantly. This configuration is also referred to as RAID-1. If one of the disks in the mirrored configuration fails, Windows 7 writes an event into the system log of the Event Viewer. The system functions normally (unless the second disk fails) until the failed disk is replaced and then the volume can be mirrored again. Mirrored volumes cost you 50% of your available storage space because of the built-in redundancy. If you mirror two 70 GB disks, you are left with just 70 GB of space rather than 140 GB.
You can make mirrored volumes more robust by installing a separate hard disk controller for each disk; technically, this is known as disk duplexing. Disk duplexing is better than disk mirroring because you alleviate the single point of failure by having one controller for each disk. Under Windows Server 2008, disk duplexing is still referred to as disk mirroring. You can create mir- rored volumes only by using dynamic disks. To create a new empty mirrored volume from unallocated space, perform the following steps:
1. Open Disk Management.
2. Right-click an area of unallocated space on a dynamic disk and select New Mirrored Volume.
3. When the Welcome to the New Mirrored Volume Wizard starts, click Next.
4. Add two or more drives to the Selected column. Specify the amount of space and click the Next button.
5. Select the appropriate drive letter and click the Next button.
Working with Volumes
6. Select NTFS as the file system. You should also specify a volume label for easier identification. You can also select a quick format and enable
file and folder compression. Click the Next button.
7. When the wizard is complete, click the Finish button. To create a mirrored volume from a boot or system volume, or to create a
mirrored volume from an existing volume that already contains data, perform the following steps:
1. Open Disk Management.
2. Right-click an existing dynamic volume and select Add Mirror.
3. From the window shown in Figure 4.5, select one of the available dynamic disks on which to create the redundant volume and click Next.
FIGURE 4.5 Creating a mirrored volume in Windows 7.
You can stop mirroring a volume by either breaking or removing the mirror. When you break a mirrored volume, each volume that makes up the mirror becomes an independent simple volume, and they are no longer fault tolerant. When you remove a mirrored volume, the removed mirrored volume becomes unallocated space on its disk, whereas the remaining mirrored vol- ume becomes a simple volume that is no longer fault tolerant. All data that
CHAPTER 4: Disk Management
was stored on the removed mirrored volume is erased. To break a mirrored volume, perform the following steps:
1. Open Disk Management.
2. Right-click one of the mirrored volumes that you want to break and select Break Mirrored Volume, as shown in Figure 4.6.
3. Click Yes in the Break Mirrored Volume message box.
FIGURE 4.6 Breaking a mirrored volume in Windows 7.
If you want to completely destroy one of the mirrored volumes and leave just one of the volumes intact, you need to perform a removal procedure instead of simply breaking the mirrored volumes. To remove a mirrored volume, per- form the following:
1. Open Disk Management.
2. Right-click a mirrored volume and then select Remove Mirror.
3. At the Remove Mirror dialog box, select the disk from which you want to completely erase the mirrored volume and turn the volume into unal-
located space. The remaining volume stays with all of its data intact as a simple volume.
Working with Volumes
4. Click the Remove Mirror button.
5. Click Yes to confirm the removal action at the Disk Management mes- sage box that appears.