Windows’ Support for Disks with Capacity Greater than 2TB

The storage industry has recently introduced storage devices with capacities which exceed 2TB (2 trillion bytes). In order for a system to fully support capacities greater than 2TB, the device must be initialized using the GPT partitioning scheme to support addressing the full range of capacity. If the user is intending to boot from one of these large disks, there is an additional requirement that the system’s base firmware interface must be using UEFI and not BIOS. This Knowledge Base article outlines Microsoft’s support statement across Windows versions since Windows XP, and the requirements necessary to address the full capacity of these devices.

Note that this document refers to disk capacity in terms of power of two, instead of power of ten, which is the most common designation on storage device capacity labels. As a result, references to “2TB” would be referring to a product labeled as having “2.2TB” of capacity.

Also note that the operating system specific behavior noted in this document also applies to the Server variants of the operating system. Thus, “Windows XP” includes Windows Server 2003 and Windows Server 2003 R2, “Windows Vista” includes Windows Server 2008, and “Windows 7” includes Windows Server 2008 R2.

Modern storage devices are addressed using a scheme called Logical Block Addressing (LBA), which is a logical arrangement of the logical sectors comprising the media. LBA0 represents the first logical sector of the device, and the last LBA represents the last logical sector of the device, with the number of LBAs representing the number of sectors within the device. To determine the capacity of the storage device, you multiply the number of logical sectors within the device by the size of each logical sector – the current standard being 512-bytes. For example, in order to achieve a device with a capacity of 2TB, you will need 3,906,250,000 512-byte sectors. However, a computer system requires 32 bits (1’s and 0’s) of information to represent this large number, and thus any number greater than what is able to be represented using 32-bits would require an additional bit – 33 bits.

The problem is that the partitioning scheme used by a vast majority of today’s modern PCs is MBR (master boot record) which places a limitation on the number of bits available to represent the number of logical sectors to be 32.

The 2TB barrier is the very manifestation of this 32-bit limitation. Since the maximum number which is able to be represented using 32-bits is 4,294,967,295, this translates to 2.199TB of capacity using 512-byte sectors, or approximately 2.2TB. As a result, capacity beyond 2.2TB is not addressable using the MBR partitioning scheme.

In order for more bits to be available for addressing, the device will instead need to be initialized with the GPT (GUID Partition Table) partition scheme which allows for up to 64-bits of logical sectors, which translates to a theoretical limitation of 9.4ZB (9.4 zetta bytes, or 9.4 billion terabytes). However, the issue with GPT is that most currently available systems are based on the aging BIOS platform which only supports booting from MBR initialized disks. In order to boot from a device initialized with the GPT partitioning scheme, your system will need to be UEFI capable. There are many systems today which ship with the capability of supporting UEFI, and Microsoft expects that most future systems will be shipping with this support. Customers should consult with their system vendor to determine support for UEFI and disks with capacities greater than 2TB.



Overall Requirements for Non-Bootable Data Volume

In order for a system to address the maximum capacity of a storage device with capacity greater than 2TB, the following requirements apply:

-          Disk initialized with the GPT Partitioning Scheme

-          Windows Version (all SKUs, either 32-bit or 64-bit):

o   Windows Vista

o   Windows 7

o   Windows Server 2008

o   Windows Server 2008 R2 (only 64 bit version available)

-          Updated storage drivers from your storage controller manufacturer

o   Specifically, if your system uses an Intel storage controller set to “RAID” mode, ensure you have the latest drivers from the Intel support site (http://www.intel.com/p/en_US/support/highlights/chpsts/imsm/) .

Overall, customers should consult with their system vendor to determine if the system supports devices greater than 2TB.



Overall Requirements for a Bootable System Volume

In order for a system to address the maximum capacity of a storage device with capacity greater than 2TB and to install Windows to and boot from the storage device, the following requirements apply.
 

-          Disk initialized with the GPT Partitioning Scheme

-          UEFI System Firmware

-          64-bit Version of Windows (all SKUs):

• Windows Vista 64-bit
• Windows 7 64-bit
• Windows Server 2008 64-bit
• Windows Server 2008 R2 64-bit

       -          Updated storage drivers from your storage controller manufacturer

• Specifically, if your system uses an Intel storage controller set to “RAID” mode, ensure you have the latest drivers from the Intel support site (http://www.intel.com/p/en_US/support/highlights/chpsts/imsm/) .

Note: Windows does not support booting of GPT initialized volumes with UEFI systems on 32-bit versions of Windows, and that that legacy BIOS systems do not support booting of GPT partitioned volumes. Consult with your system vendor to determine if the system supports UEFI and booting of devices greater than 2TB.


Support Matrix

The tables below indicate Microsoft’s support for the various concepts discussed in the above sections, summing up to the overall support statement for disks with capacities greater than 2TB.

Table 1: Windows support for partitioning schemes as data volumes

* Note: “Hybrid-MBR” is an alternative style of partitioning which is not supported by any version of Microsoft Windows.

Table 2: Windows support for system firmware


Table 3: Windows support for combinations of boot firmware and partitioning schemes for the boot volume


Table 4: Windows support for large capacity disks as non-booting data volumes

** Capacity beyond 2TB cannot be addressed by Windows if the disk is initialized using the MBR partitioning scheme. For example, with a 3TB single disk initialized with MBR, Windows can create partitions up to the first 2TB, but the remaining capacity cannot be addressed and therefore cannot be utilized. 



How to Initialize Data Disk with GPT

The below steps illustrate how to initialize a fresh disk with the GPT portioning scheme to help ensure Windows can address the maximum available capacity. Ensure you backup any important data before attempting the below steps.

1.       Press the Windows key on your keyboard. The Start menu should appear.

2.       In the search box, type in “diskmgmt.msc”, and a search result under “Programs” should appear. Right click diskmgmt.msc and press “Run as Administrator”. If necessary, enter the credentials for a user account with Administrator privileges.

3.       When a non-initialized disk is detected by Windows, you should see the following popup prompting you to initialize the disk:



4.       Select the “GPT (GUID Partition Table)” option and press OK. (NOTE: By selecting this option, this disk will not be recognized by Windows OS versions including and prior to Windows XP.)

5.       Your disk should be initialized. To confirm this, the status below the disk should indicate the disk is “Online”.



6.       Now that the disk has been initialized, you will need to create a partition and format that with a file system in order to store data on the disk, and to assign a drive letter to. Right click the unallocated space to the right of the “Disk” label, and press “New Simple Volume…”. The wizard will guide you through the process of creating the partition, choosing a name for the volume, formatting it, and assigning a drive letter.



How to Convert MBR Disk to GPT

If you have previously initialized the disk with the MBR partitioning scheme, the below steps illustrate how to convert the disk to be initialized with the GPT partitioning scheme. Ensure you backup any important data before attempting the below steps.

1.       Press the Windows key on your keyboard. The Start menu should appear.

2.       In the search box, type in “diskmgmt.msc”, and a search result under “Programs” should appear. Right click diskmgmt.msc and press “Run as Administrator”. If necessary, enter the credentials for a user account with Administrator privileges.

3.       The Disk Management interface should appear. In this example, the user has a 3TB disk previously initialized using the MBR partitioning scheme – in the diagram, this device is labeled “Disk 1”.



4.       You can see in the above diagram, there are two separate “Unallocated” portions of the device. This separation indicates that the first 2TB can be utilized, but the remaining space is left un-addressable due to the MBR partitioning scheme 32-bit addressing space limitation discussed in a previous section. In order to enable the system to fully address the total capacity of the storage device, you will need to convert the disk to use the GPT partitioning scheme.

5.       Right click the intended disk – the Disk label on the left. Select the “Convert to GPT Disk” option.

6.       You should immediately see that the full amount of space is available for usage as shown here.



7.       Now that the disk has been initialized with full capacity, you will need to create a partition and format that with a file system in order to store data on the disk, and to assign a drive letter to. Right click the unallocated space to the right of the “Disk” label, and press “New Simple Volume…”. The wizard will guide you through the process of creating the partition, choosing a name for the volume, formatting it, and assigning a drive letter.



Known Issues/Limitations

As the transition to single-disk capacity greater than 2TB has occurred fairly recently, Microsoft has conducted an internal investigation as to Windows’ support for these large disks. The below are a list of issues which have been discovered thus far, and are applicable to all versions of Windows up to and including Windows 7 with Service Pack 1, and Windows Server 2008 R2 with Service Pack 1:



Incorrect Storage Driver Handling of Single-Disk Capacity Greater than 2TB

Microsoft has discovered that certain storage drivers do not fully support single-disk capacities greater than 2TB. The behavior of some drivers may include:

-          Overflow of numerical capacity beyond 2TB, resulting in only able to address the remainder of the capacity beyond 2TB. For example, with a 3TB disk, the available capacity may be 1TB.

-          Truncation of capacity beyond 2TB, resulting in a maximum of 2TB of addressable space. For example, with a 3TB disk, the available capacity may be 2TB.

-          Storage device is not properly detected, and does not show up either in Device Manager or Disk Management.

Many storage controller manufacturers have updated drivers with support for capacities greater than 2TB available for download. Contact your storage controller manufacturer or OEM to determine support for single-disk capacities greater than 2TB, and if there are any available downloads to provide support. 



SCSI Sense Data

When a disk encounters errors related to un-readable or un-writeable sectors, it reports the error along with SCSI Sense Data to the operating system. SCSI sense data may contain information about LBA for sectors which were considered to be un-readable or un-writeable. For LBA address space greater than 2TB, it requires SCSI sense data in Descriptor format, which is not supported by Microsoft Windows 7 and Windows Server 2008 R2, which retrieve SCSI sense data in the Fixed format. As a result, retrieved SCSI Sense Data would either not contain, or contain incorrect values detailing bad sector information. Administrators should take note of this limitation when looking for bad sector LBA information recorded in Windows System Event Log.

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