Mirroring Windows Server 2008 GBT and MBR Boot and System Disks

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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 mirroing 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 boots from MBR disk partitions and 64-bit systems can only boot from GPT partitions.

Each partition style has different capabilities and partitioning styles. Of most significance is the fact that the two partition styles have very different configurations in terms of special mandatory partitions required in order to store data. In addition, other mandatory partitions are required on each disk style in order to operate as boot and system disks. In terms of MBR disks a master boot record (MBR) partition is required. On GPT disks, EFI system (ESP) and Microsoft Reserved (MSR) partitions must be present in order for the disk to be bootable. It is important, therefore, that these partitions are created as part of the system disk mirroring configuration process.

Mirroring Boot and System Volumes on an MBR Disk

The process of mirroring boot and system volumes on Windows Server 2008 MBR disks is considerably more straight forward 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 now 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 drive available on the system. Select the desired disk (in this case disk 1) as shown below:

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) and Microsoft Reserved (MSR) partitions. 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.