Windows 7 / Getting Started

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Managing GPT Disk Partitions on Basic Disks

GPT disks can have the following types of partitions:

• ESP
• MSR partition
• Primary partition
• Logical Disk Manager (LDM) Metadata partition
• LDM Data partition
• OEM or Unknown partition

Each of these partition types is used and managed in different ways.

ESP

An Itanium-based computer must have one GPT disk that contains an ESP. This partition is similar to the system volume on an x86-based computer in that it contains the files that are required to start the operating system. Windows Server 2008 creates the ESP during setup and formats it by using FAT. The partition is sized so that it is at least 100 MB in size or 1 percent of the disk up to a maximum size of 1000 MB.

The ESP is shown in Disk Management but isn't assigned a drive letter or mount point. All Disk Management commands associated with the ESP are disabled, however, and you cannot store data on it, assign a drive letter to it, or delete it by using Disk Management or DiskPart. The ESP has several directories that contain the operating system boot loader, such as Ia64ldr.efi , and other files that are necessary to start the operating system as well as utilities such as Diskpart.efi and Nvrboot.efi. Other directories are created as necessary by the operating system.

The only way to access these directories is to use the EFI firmware's Boot Manager or the MountVol command. If you access the ESP, don't make changes, additions, or deletions unless you've been specifically directed to by a Microsoft Knowledge Base article or other official documentation by an OEM vendor. Any changes you make could prevent the system from starting.

Although the ESP is normally created for you automatically when you install Windows Server 2008, there are some limited instances when you might be directed to create an ESP after installing an additional GPT disk on a server, such as when you want to use the new disk as a boot device rather than the existing boot device. You can create the necessary ESP by using DiskPart. Select the disk you want to work with, and then type the following command: create partition efi size=N, where N is at least 100 MB or 1 percent of the disk, up to a maximum size of 1000 MB. After you create the partition, follow the vendor-directed or Microsoft-directed guidelines for preparing the partition for use. Never create an ESP unless you are directed to do so, however. One instance in which you must create an ESP is when you want to establish and boot to mirrored GPT disks. Here, you must prepare the second disk of the mirror so that it can be booted, and you do this by creating the necessary ESP and MSR partition.

MSR Partitions

An Itanium-based computer must have an MSR partition on every GPT disk. The MSR partition contains additional space that might be needed by the operating system to store metadata. For example, when you convert a basic GPT disk to a dynamic GPT disk, the Windows operating system takes 1 MB of the MSR partition space and uses it to create the LDM Metadata partition, which is required for the conversion.

The MSR partition is not shown in Disk Management and does not receive a drive letter or mount point. The Windows operating system creates the MSR partition automatically. For the boot disk, it is created along with the ESP when you install the operating system. An MSR partition is also created automatically when a disk is converted from MBR to GPT and any time you access a GPT disk that doesn't already have an MSR partition in Disk Management or DiskPart.

If a GPT disk contains an ESP as the first partition on the disk, the MSR partition is usually the second partition on the disk. If a GPT disk does not contain an ESP, then the MSR partition is typically the first partition on the disk. However, if a disk already has a primary partition at the beginning of the disk, the MSR partition is placed at the end of the disk.

The MSR partition is sized according to the size of the associated disk. For disks up to 16 GB in size, it normally is 32 MB in size. For all other disks, it normally is 128 MB in size.

The MSR partition is normally created for you automatically when you install Windows Server 2008. It can also be created automatically when you access a secondary GPT disk that doesn't already have an MSR partition in Disk Management or DiskPart. You shouldn't attempt to create a Microsoft Reserved partition unless you are directed to by vendor-specific or Microsoft-specific documentation. In this case, you can use DiskPart to create the partition. Select the disk you want to work with, and then type the following command: create partition msr size=N, where N is 32 for disks up to 16 GB in size and 128 for all other disks.