Partitioning GPT Disks on UEFI systems


Tom’s Hardware (December 30, 2009 by Patrick Schmid and Achim Roos)

“You need a 64-bit version of Windows XP Professional (with the same core operating system version as Windows Server 2003 SP1), Vista, or Windows 7, to get full GPT support for drives that offer more than 2TB capacity. GPT offers the following features:

  • Maximum raw partition capacity of 18 exabytes
  • The Windows NTFS file system is limited to 256TB each: with up to 2^64 logical blocks in length and a physical cluster size of 65536-bytes (formatting with an allocation unit of 64 KiB sector groups required!)
  • Implementation restriction of 128 partitions per disk (limited by the amount of space reserved for partition entries in the GPT)
  • Primary and backup partition tables available for redundancy
  • Well-defined and self-identifying partition format
  • Each partition has a unique ID to avoid identifier collisions (“GUID” partition table)

Here is an overview of your possible partitioning options and actions on GPT and MBR:

32-bit Windows 64-bit Windows
GPT MBR GPT MBR
Boot No Yes Yes No
Read No Yes Yes Yes
Write No Yes Yes Yes

UEFI support becomes relevant for drives >2TB. It must be present to enable booting from such large partitions provided the other prerequisites (64-bit Windows and GPT) are met.

GPT Details on Windows x64
GPT will automatically install the EFI System Partition (ESP), which contains the boot loader, EFI drivers, and all other necessary files for booting the system (such as boot.ini, HAL, and NT Loader). It utilizes the GUID Partition Table rather than the master boot record. The ESP is 1% of the drive capacity, or a minimum size of 100MB and a maximum size of 1,000MB.

GPT systems will also be equipped with an MSR partition, which stands for Microsoft Reserved. Since GPT partitions don’t allow hidden sectors, Windows utilizes this reserved space for operating system use. If you decide to convert a basic disk into a dynamic disk, Windows will use the MSR partition, shrink its size, and create the dynamic disk database using available space. On drives smaller than 16GB, the MSR partition will be only 32MB. For larger disks, it will consume 128MB.”

Chatwin says: Even if your system is GPT-compliant and created using the necessary partition, you will still need UEFI support to be able to boot from a large volume (UEFI = Unified Extensible Firmware Interface).

In the second place support for 48bit LBA also requires Advanced Format CDB block re-alignment, enabled with an internal PCI-E Host Bus Adapter Card (by using the native Windows AHCI drivers only), your RAID controller and/or HDD device drivers. Here is where Long LBA addressing comes in…

Long LBA addressing increases the number of bytes used to define the LBA in the Command Descriptor Block (CDB). System must support at least 16-byte Command Descriptor Blocks (CDBs) or 32 bytes (Protection Information commands only) and Dynamic Sense Data to access the LBA counts above 2.1TB. Eight LBA address bytes are provided in 16- and 32-byte CDBs. This is a doubling of the 4 bytes in 10-byte commands (http://www.seagate.com/docs/pdf/whit…_readiness.pdf).

Installation requirements
1. Windows XP Professional with SP2 for Windows Server 2003 64-bit, Vista 64-bit, Windows 7 64-bit for GPT.
2. UEFI booting support since Windows Vista with Service Pack 1 (64-bit only).
3. Motherboard with UEFI 2.x implementation for boot drives on a partition larger than 2.2 TB.
4. Windows 7 (SP1) is supposed to understand AF drives, and correctly aligns partitions. Without the updates in a hotfix, Windows can’t detect the drive’s physical sector size, and Windows Update (and some other features) fail. Microsoft explanation and hotfix link: An update that improves the compatibility of Windows 7 and Windows Server 2008 R2 with Advanced Format Disks is available.
5. SP1 with hotfix aren’t correctly updating the storage driver, so it can’t report sector size to Windows. The clue here is that fsutil still reports “bytes per physical sector” as “<Not Supported>”. You can fix this issue to manually install the latest Intel driver (9.6 or later): Intel® Rapid Storage Technology.
6. Alignment instructions for installing XP64:

  • Use LSoft Active Boot Disk Suite (based on WinPE 3.1) to create a partition with an offset of 2048KB, format with 4K sectors and reboot.
  • Replace with XP64 SP2 installation DVD and install without altering the partition parameters.
  • After final installation reboot and use Paragon Partition Manager Server (WinPE 3.0 recovery environment) to convert cluster size from 4KB to 64KB.
  • Shutdown and start from primary HDD partition.

Paragon just introduces a new solution: Migrate to UEFI.
“It’s a simple four-step Copy Hard Disk Wizard that transfers a 64-bit Windows Vista/7 initially installed on an MBR disk in the BIOS mode to a GPT disk and the UEFI mode, thus opening up all benefits of the GPT+UEFI configuration, including support of a high-capacity 2.2TB+ hard drive for use as the primary system HDD.

Become an early adopter and download this component for free>>

Home and small-office users who try to move their 64-bit Windows Vista or Windows 7 software environments from the dated MBR/BIOS configuration to a modern GPT/UEFI platform find that you can’t just change the partitioning scheme and enable UEFI without reinstalling the operating system from scratch. The problem is that Windows Disk Management supports conversion to GPT for empty drives only, so you’ve got no way of converting the system drive to GPT without losing data. Besides Windows Management tools do not provide an option to adjust boot files for UEFI, making it impossible for users transferring established data or system components within a single computer directly from a BIOS boot mode to a UEFI-based mode.

Paragon Migrate to UEFI can help you tackle both issues with minimal effort. Some important benefits:

  • Automatically adjusts Windows OS to start up in the UEFI mode
  • Automatically creates a GPT partitioning scheme during migration
  • Supports AFD (Advanced Format Drive) disks (mixed 512B/4K sector scheme only, including virtual)
  • The source system remains intact and can be loaded in the BIOS mode at any time
  • Copy operation is run without the system restart by employing Microsoft VSS technology”
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About Chatwin
This is my website: http://rdwaal.com/, dedicated to my personal designed computer with relevant technological know-how which I learned during my testing and fine tuning period. Concept PC “The Force” evolved in 21 months (minus 7 days) from only a slight idea, till an amazing workstation with remarkable capabilities. It wasn’t labor for me, nor suffering or hard work. It was fun.... If you’re interested in a custom build computer, based on your own preferences, contact me for further information. I only use the best hardware with an acceptable price level. I can assure the best performance within your budget and an unique (thoroughly tested) concept computer/server.

2 Responses to Partitioning GPT Disks on UEFI systems

  1. Kenneally says:

    Fantastic site you have here but I was curious about if you knew of any user discussion forums that cover the same topics talked about here? I’d really like to be a part of community where I can get responses from other experienced people that share the same interest. If you have any suggestions, please let me know. Thanks!

  2. Doyan says:

    Thank you, I’ve recently been looking for info approximately this topic for a long time and yours is the best I’ve discovered so far. However, what concerning the conclusion? Are you positive in regards to the source?

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