Managing Windows Server 2012 Storage and File Systems : Storage Management (part 11) - Managing GPT disk partitions on basic disks

7/3/2013 4:16:28 AM

5. 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

EFI-based computers must have one GPT disk that contains an ESP. This partition is similar to the system volume on a computer with an MBR boot disk in that it contains the files that are required to start the operating system. Windows Server 2012 creates the ESP during setup and formats it by using FAT. Normally, the partition is sized so that it is at least 100 MBs in size or 1 percent of the disk, up to a maximum size of 1000 MBs.

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 2012, 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 MBs or 1 percent of the disk, up to a maximum size of 1000 MBs. 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 partitions.

MSR partitions

EFI-based computers that use GPT for boot must have an MSR partition on every GPT disk. The MSR partition contains additional space that might be needed by the operating system to perform disk operations. 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, 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 GBs in size, it normally is 32 MBs in size. For all other disks, it normally is 128 MBs in size.

The MSR partition is normally created for you automatically when you install Windows Server 2012. 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 Disk Part 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 GBs in size and 128 for all other disks.

Primary partitions

You create primary partitions on basic disks to store data. GPT disks support up to 128 partitions, which can be a mix of required and optional partitions. Every primary partition you create appears in the GUID partition entry array within the GPT header. If you convert a basic disk that contains primary partitions to a dynamic disk, the primary partitions become simple volumes, and information about them is then stored in the dynamic disk database and not in the GUID partition entry array.

To create a primary partition, complete the following steps:

In Disk Management Graphical View, press and hold or right-click an area marked Unallocated on a basic disk, and then choose New Simple Volume. This starts the New Simple Volume Wizard. Tap or click Next.
The partition is created as a primary partition automatically. Use the Assign Drive Letter Or Path page to assign a drive letter or path. You can also choose Do Not Assign A Drive Letter Or Drive Path if you want to create the partition without assigning a drive letter or path. Tap or click Next.
Use the Format Partition page to set the formatting options.
Tap or click Next. The final page shows you the options you’ve selected. If the options are correct, tap or click Finish. The wizard then creates the partition and configures it.

LDM Metadata and LDM Data partitions

Windows Server 2012 creates LDM Metadata and LDM Data partitions when you convert a basic GPT disk to a dynamic GPT disk. The LDM Metadata partition is 1 MB in size and is used to store the partitioning information needed for the conversion. The LDM Data partition is the partition in which the actual dynamic volumes are created.

The LDM Data partition is used to represent sections of unallocated space on the converted disk as well as sections that had basic partitions that are now dynamic volumes. For example, if a disk had a primary boot partition that spanned the whole disk, the converted disk will have a single LDM Data partition. If a disk had a boot partition and other primary partitions, it will have two LDM Data partitions after the conversion: one for the boot volume, and one for all the rest of the partitions. Although the LDM Metadata and LDM Data partitions are not shown in Disk Management and do not receive drive letters or mount points, you are able to use this space by creating primary partitions as discussed in the previous section.

OEM or unknown partitions

GPT disks can have partitions that are specific to OEM implementations, and your vendor documentation should describe what they are used for. The Windows operating system might display these partitions in Disk Management as Healthy (Unknown Partition). You cannot, however, manipulate these partitions in Disk Management or DiskPart. Additionally, if an unknown partition lies between two known partitions on a GPT disk, you typically can’t convert the disk from the basic disk type to the dynamic disk type.