GUID Partition Table and 2 Terabyte (or larger) harddrives / Technical / Forums

Morgue[FLB]

:: Mortal Wombat ::

Level 10

16 years ago

In Windows 7, when you want to install a harddrive that is 2 terabytes or larger in size, you will be asked by the Disk Management Console what partition style you'd like to use for the new disk:

1270555339 59 FT0 Interesting Message About 2tb

1270555339 59 FT0 Interesting Message About 2tb

This is because the MBR (Master Boot Record) partition style is limited to a maximum of 2 terabytes.

At http://en.wikipedia.org/wiki/GUID_Partition_Table, Wikipedia says:

In computer hardware, GUID Partition Table (GPT) is a standard for the layout of the partition table on a physical hard disk. Although it forms a part of the Extensible Firmware Interface (EFI) standard (Intel's proposed replacement for the PC BIOS), it is also used on some BIOS systems because of the limitations of MBR partition tables, which restrict maximum disk size to 2 TiB.

Currently, support for GPT among common Microsoft operating systems is limited. 64-bit Windows XP, 64-Bit Windows Server 2003, Windows Server 2003 SP1 (all versions), Windows Vista, Windows Server 2008 and Windows 7 support GPT, but NOT as bootable drives. So if you want your 2 terabyte harddrive to be bootable, you need to use the MBR partition style. However, if you want to use your 2 terabyte (or larger) drive only for data storage, consider picking the GPT style instead:

As of 2010[update], MBR-based partition table schemes insert the partitioning information in the master boot record (MBR) itself (which on BIOS system is also the container for code that begins the process of initializing the disk). In GPT, partition table information is stored in the GPT header, but to maintain compatibility, GPT retains the MBR entry as the first sector on the disk followed by a Primary Partition Table Header, the actual beginning of GPT.

Like modern MBRs, GPT uses logical block addressing (LBA) in place of the historical cylinder-head-sector (CHS) addressing. Legacy MBR information is contained in LBA 0, the GPT header is in LBA 1, and the partition table itself follows. 64-bit Windows operating systems reserve 16,384 bytes (or 32 sectors) for the GPT, leaving LBA 34 as the first usable sector on the disk.

Apple warns:[2] "Do not assume that the block size is always going to be 512 bytes." Modern storage devices such as solid-state drives may contain 1024-byte LBAs and some magneto-optical (MO) drives use 2048-byte sectors (but MO drives are typically not partitioned). Hard disk manufacturers are planning to transition to 4096-byte sectors, but as of early 2010, the first such drives employ firmware that presents the illusion of 512-byte sectors to the OS. [3]

Drives which boot Intel-based Macs are typically formatted with a GUID Partition Table, rather than with the Apple Partition Map.

GPT also provides redundancy, writing the GPT header and partition table both at the beginning and at the end of the disk.

Svg

Synthetic_Darkness

Godlike

Level 7

16 years ago

Thats cool. I knew about the 2 tb MBR size limit, but I guess it never really was an issue for me.

Good find Morgue.

Morgue[FLB]

:: Mortal Wombat ::

Level 10

15 years ago

UPDATE:

Edited my original post to reflect the fact that 32-Bit Windows XP does NOT support GPT-formatted drives (although 64-Bit Windows XP does).

So in order to access a GPT-formatted drive in 32-Bit Windows XP, you'd have to run virtual machine software like VMWare, VirtualBox, Microsoft Virtual PC (etc), and run an emulated installation of 64-Bit Windows XP or 32-Bit Windows 7.

Alternatively, you could download and install Paragon Software's HFS for Windows 7.5. They are currently giving away 50 000 licenses, so you better hurry if you want one :)

http://www.paragon-software.com/home/hfs-windows/giveaway.html

After installing HFS for Windows (including the unsigned ''Disk'' drivers that it installs) and rebooting, I found that my GPT-formatted disk was accessible in 32-Bit Windows XP.

!wave

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