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The focus of this chapter is the mirroring of boot and system disks on Windows Server 2008. It is important to note that the steps necessary for mirroring system disks differs depending on whether the disk uses the MBR or GPT partitioning style. As such, this chapter will cover the steps necessary to mirror both types of Windows Server 2008 system disk.
== An Overview of GPT and MBR Partition Styles ==
Before a Windows Server 2008 system disk can be mirrored it is important to identify the partition style used by the disk as this will dictate the technique used to create the mirror. In order for a disk to be used to store data it must first have partitions created on it. These partitions are then
formated with a particular file system (FAT, FAT32 , NTFS) and used either as a basic disk or as dynamic disk. Obviously, the operating system needs some mechanism for organizing and managing these disk partitions and Windows Server 2008 provides two such partitioning styles known as Master Boot Record (MBR) or GUID Partition Table (GPT).
The MBR style was originally developed for x86-based computer systems and is by far the most common style in use at present. GPT, on the other hand, was originally developed for 64-bit Itanium based systems. With the arrival of Windows Server 2008 both x86 32-bit and 64-bit systems support MBR and GPT partition styles. It is important to note, however, that 32-bit systems can only boot from MBR disk partitions and 64-bit systems can only boot from GPT partitions.
== Mirroring Boot and System Volumes on an MBR Disk using Disk Management ==
The process of mirroring boot and system volumes on Windows Server 2008 MBR disks is considerably more straightforward than on GPT disks. For the purposes of this chapter we will be working with a system containing
2 disk drives. Disk 0 is the system disk and disk 1 is an unallocated disk installed for the purpose of mirroring the system disk. This process can be performed using either the Disk Management interface or from the command prompt using the '''diskpart''' tool (covered in the next section). The Disk Management interface can be accessed either from the Server Manager or Computer Management tools. To launch the Server Manager, open the Start menu and click on the Server Manager option, or click on the Server Manager icon in the task bar. Alternatively launch Computer Management from Start -> All Programs -> Administration Tools -> Computer Management or run '''compmgmt.csc''' at the command prompt or in a Run dialog.
Before the system disk can be mirrored it must first be converted to a dynamic disk. To achieve this right click on the system drive in the Disk Management graphical view, select ''Convert to Dynamic Disk...'' from the popup menu and follow the instructions in the resulting dialog to perform the conversion.
With the system disk now a dynamic disk, all that needs to be done is to add the new disk as a mirror of the system disk. To achieve this right click on the system volume in the Disk Management graphical view and select ''Add Mirror...'' from the popup menu. The resulting ''Add Mirror'' dialog will list the disk drives available on the system. Select the desired disk (in this case disk 1) as shown below:
[[Image:windows_server_2008_select_system_mirror_disk.jpg|Selecting a Mirror Disk for a Windows Server 2008 system volume]]
With a suitable mirror disk selected, click on ''Add Mirror'' to begin the resynching process. During this phase the operating system will copy all the files from the original system volume (including System, Boot, PageFile and Crash Dump) to the mirror disk. It will also create the master boot record (MBR). Finally, Windows will add the mirror as a secondary boot option in the Boot Manager such that it can be selected when the system is rebooted. During the reboot process the boot menu will appear listing the shadow system partition as ''Microsoft Windows Server 2008 - secondary plex'':
[[Image:windows_server_2008_second_plex_boot.jpg|The Windows Server 2008 boot menu with system mirror listed as secondary plex]]
In the above output disk 0 is the current system disk and disk 1 is the disk to used as the shadow system disk. If the disks are not yet dynamic they need to be converted before the remainder of the mirroring set up and can be completed:
In the above example the system volume is listed as ''Volume 0''. To mirror this volume, select the volume and then add disk as a mirror using the ''add disk='' command:
This will initiate the resynching process which may take some time depending on the size of the system volume. When a ''list volume'' command is run the volume will be listed as ''Rebuild'' until the resynching is complete:
In the above output, Partitions 1 and 3 are the EFI and MSR partitions respectively. In order to accurately mirror the system disk these partitions also need to created on the mirror disk using the ''create partition'' command
Once a drive letter have been assigned, open a second command prompt window
, format the partition. Note that it may be necessary to laucnh the command prompt with elevated privileges. To do this locate the command prompt in the Start menu, right click on it and select ''Run as Adminsitrator''.
DISKPART> select disk 0
DISKPART> add disk=1
This will initiate the mirroring process which may take some time depending on the size of the system volume as Windows Server 2008 carries out the resynching process. In addition to resynching the mirrored volumes Windows will also add the mirrored disk to the boot configuration such that it will listed as the ''Microsoft Windows Server 2008 - secondary plex'' option on the boot menu next time the system is booted.