Thursday, April 12, 2012

What is GPT ?

Globally Unique Identifier Partition Table Format
It is a framework of disk partition based on Expandable Firmware Interface (EFI) in Itanium. Compared with Master Boot Record (MBR), GPT has more advantages. It permits every disk having up to 128 partitions and supports maximum volume of 18KM bytes. And primary disk partition table and backup of disk partition table can be used in redundancy. In addition, it also supports sole disk and partition ID (GUID)

Comparison of GPT and MBR

Master  Boot Record supports the maximum volume of 2TB( terabytes) and every diskhas 4 primary partitions( or 3 primary partitions , 1 extended partition and an unlimited logical driver ) at most. Compared with MBR, GPT of GUID partition supports the maximum volume of 18TB (terabytes) and every disk has 128 partitions at most. Different from disk in MBR partition, the data of operating platform is located in partitions in GPT, but not located in non-partitioned or implicit sectors. Besides, there are spare primary partition tables and backup of partition tables to improve the integrity of data structure in disks of GTT partition. In "disk management", on the tab "VOL" in the Dialog of disk attributes, the disk of GPT partition is displayed as GUID partition table(GPT) disk and disk of MBR partition is displayed as MBR disk. The operations supported by MBR can be implemented in GPT disk if the following accident occurs. When the computer based on x84 and the computer based on x86 having Windows Server 2003 with Service Pack 1 (SP1) are operated, the operating system must be located in MBR disk and other disks can be MBR or GPT. In the computer based on Itanium, the loading program of operating system and boot partition must be located in GPT disk. And other disks can be MBR or GPT.

Features of GPT
GPT can not be transfered to computer based on x86 running Windows NT 4.0, Windows 2000, Windows XP or Windows Server 2003. However, GPT disk can be transfered from computer based on x64 or computer based on x86 running Windows Server 2003 with SP1 to computer based on Itanium running Windows Server 2003 or Windows XP, or vice versa.

The Windows edition based on Itanium can not be applied to transfer GPT disk from computer based on Itnium to computer based on x64 or computer based on x86 running Windows 2003 with SP1 and to start he operating system. In the computer based on non-Itanium, GPT disk must be applied only for data storage.

MBR disk and GPT disk can coexist in single group of dynamic disks. And basic GPT and MBR disks can be mixed to use but they are not a part of the disk group.. MBR and GPT disks can simultaneously be applied to build mirrored volume, stripped volume, spanned volume and RAID 5 volume. But the limits of Cylinder alignment make it difficult to build mirrored volume. The MBR disk can be mirrored to GPT disk to avoid cylinder alignment.Disadvantages of GPTMBR disk can be transfered into GPT disksand only the disk is empty, can GPT disk be transfered into MBR disk. Of course, the third-party tools must be used. And MiniTool Partition Wizard is recommended. It can easily exchange disk types of MBR and GPT. More help informations are provided in How to initialize disk to GPT disk or MBR disk?

GPT is not in support of mirror of EFI system partition. The command bootcfg must be applied to copy EFI system partition.

GPT partition type can not be applied in removable media or cluster disk connected to Fibre Channel trunk or sharing SCSI applied in cluster service.
The command DiskPart.exe can be applied to run utility program or EFI program (Diskpart.efi ) to built partitions in basic GPT disk.

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