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What is a GPT disk? How to backup a GPT disk?


GPT & UEFI

The GUID Partition Table (GPT) was introduced as part of the Unified Extensible Firmware Interface (UEFI). GPT provides a more flexible specification for partitioning disks than the older Master Boot Record (MBR) partitioning scheme for computers.


Disk Partitions

A partition is a contiguous space of storage on a physical or logical disk that functions as if it were a physically separate disk. Partitions are visible to the system firmware and the installed operating systems. For example, partitions are represented as drive letters in Windows (such as C:, D:).


GPT Partition & MBR Partition

MBR disks support only four partition table entries. If more partitions are wanted, a secondary structure known as an extended partition is necessary. Extended partitions can then be subdivided into one or more logical disks.


GPT disks can grow to a very large size. The number of partitions on a GPT disk is not constrained by temporary schemes such as container partitions as defined by the MBR Extended Boot Record (EBR).


The GPT disk partition format is well defined and fully self-identifying. Data critical to platform operation is located in partitions and not in unpartitioned or "hidden" sectors. GPT disks use primary and backup partition tables for redundancy and CRC32 fields for improved partition data structure integrity. The GPT partition format uses version number and size fields for future expansion.


GPT & GUID

Each GPT partition has a unique identification GUID and a partition content type, so no coordination is necessary to prevent partition identifier collision. Each GPT partition has a 36-character Unicode name. This means that any software can present a human-readable name for the partition without any additional understanding of the partition.


Basic GPT Disk

Basic disks are the storage types most often used with Windows. The term basic disk refers to a disk that contains partitions, such as primary partitions and logical drives, and these in turn are usually formatted with a file system to become a volume for file storage.


The GPT basic disk is illustrated in the following figure.

GPT disk picture and diagram

GPT Partition Size

In theory, a GPT disk can be up to 2^64 logical blocks in length. Logical blocks are commonly 512 bytes in size.


The maximum partition (and disk) size is a function of the operating system version. Windows XP and the original release of Windows Server 2003 have a limit of 2TB per physical disk, including all partitions. For Windows Server 2003 SP1, Windows XP x64 edition, and later versions, the maximum raw partition of 18 exabytes can be supported. (Windows file systems currently are limited to 256 terabytes each.)


The specification allows an almost unlimited number of partitions. However, the Windows implementation restricts this to 128 partitions. The number of partitions is limited by the amount of space reserved for partition entries in the GPT.


All FarStone Backup Recovery products support GPT disk

FarStone backup recovery products support GPT backup, GPT imaging, move GPT disk, clone GPT, copy and restore GPT disks.


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