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GUID partition table

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

GUID partition table

The GUID partition table (GPT) disk partitioning style supports volumes up to 18 exabytes in size and up to 128 partitions per disk, compared to the master boot record (MBR) disk partitioning style, which supports volumes up to 2 terabytes in size and up to 4 primary partitions per disk (or three primary partitions, one extended partition, and unlimited logical drives). Unlike MBR partitioned disks, data critical to platform operation is located in partitions instead of unpartitioned or hidden sectors. In addition, GPT partitioned disks have redundant primary and backup partition tables for improved partition data structure integrity.

On the Volumes tab in the disk properties dialog box in Disk Management, disks with the GPT partitioning style are displayed as GUID Partition Table (GPT) disks, and disks with the MBR partitioning style are displayed as Master Boot Record (MBR) disks. You can perform the same tasks on GPT disks as you can on MBR disks with the following exceptions:

  • On x86-based computers running Windows Server 2003 with Service Pack 1 (SP1) and on x64-based computers, the operating system must reside on an MBR disk. Other hard disks can be either MBR or GPT.

  • On Itanium-based computers, the operating system loader and boot partition must reside on a GPT disk. Other hard disks can be either MBR or GPT.

  • You cannot move GPT disks to x86-based computers running Windows NT 4.0, Windows 2000, Windows XP, or Windows Server 2003. However, you can move GPT disks from either x86-based computers running Windows Server 2003 with SP1 or x64-based computers to Itanium-based computers running Windows Server 2003 or Windows XP, or vice versa.

  • You cannot move a GPT disk with an Itanium-based version of Windows from Itanium-based computers to either x86-based computers running Windows Server 2003 with SP1 or x64-based computers, and then boot that operating system. GPT disks that are used in non-Itanium-based computers must be used for data storage only.

  • You can have both MBR and GPT disks in a single dynamic disk group. You can also have a mix of basic GPT and MBR disks, which are not part of disk groups. You can create mirrored, striped, spanned and RAID-5 volumes using a combination of MBR and GPT disks, but the MBR cylinder alignment restriction may cause some difficulties in creating mirrored volumes. Always mirror the MBR disk to the GPT disk to avoid cylinder alignment difficulties.

  • You can convert an MBR disk to a GPT disk and vice versa only if the disk is empty.

  • Mirroring the EFI System partition is not supported. Instead, you must clone the EFI System partition using the bootcfg command.

  • You cannot use the GPT partitioning style on removable media, or on cluster disks that are connected to shared SCSI or Fibre Channel buses used by the Cluster service.

You can create partitions on basic GPT disks using the DiskPart.exe command-line utility, Disk Management, or the EFI firmware utility Diskpart.efi. For more information about DiskPart.exe, see DiskPart. For more information about the Disk Management snap-in, see Disk Management overview. For more information about Diskpart.efi, see the Intel Web site.

In a system recovery scenario on an Itanium-based computer, see the manufacturer's documentation that came with the computer for recreating or restoring a GPT disk.

For more information about managing GPT and MBR disks, see Extensible Firmware Interface or Disk Management at the Microsoft Windows Resource Kits Web site.

Web addresses can change, so you might be unable to connect to the Web site or sites mentioned here.

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