Disk Partitions

In Windows 7 systems we find two different partitioning systems. These are the Master Boot Record (MBR) and the Globally Unique Identifier Partition Table (GPT) styles. While MBR is supported by all versions of Windows, GPT is only supported on Windows Vista, Windows 7, Windows Servers 2003 and 2008, and 64-bit versions of Windows XP. GPT offers several advantages over MBR such as, it can support up to 128 partitions while MBR supports only four, GPT is more reliable as it is aware of the modern disks geometries, GPT supports larger partitions – up to 18 Exabytes in theory and uses primary & backup partition tables for redundancy.

When using GPT partitions it is worth noting that larger partition sizes can have side-effects such as, take longer to check (running ChkDsk) and they are not compatible with all operating systems! Also, to boot from a GPT disk, the computer must support the Extensible Firmware Interface (EFI). Remember, that all BIOS based systems must boot from an MBR disk. Removable media cannot be partitioned with the GPT style.

Working with partitions requires you to have Administrator or Backup Operator privileges. You can use either the Disk Management graphical tool or the Diskpart command-line utility for all disk related tasks. Plan disk partitions according to your requirements as it may require a full data backup to convert disks at a later time. For example, BitLocker Drive Encryption has specific partitioning requirements.

By default, a newly installed disk is set as basic MBR, that is, it uses the MS-DOS style MBR partition tables to store the disk partitioning information. It is recommended to leave disk as basic if you do not require the features provided by dynamic disks. Dynamic disks provides additional features such as, the ability to span a volume across multiple disks and the ability to create stripe sets that gives you disk redundancy and better I/O performance. With basic disks you can create new partitions, delete partitions and extend or shrink existing partitions. With dynamic disks you can create spanned volumes, striped volumes, mirrored volumes and RAID-5 volumes. However, with dynamic disks there are serious implications when moving disks from one computer to another. When you need to move dynamic disks to another computer you have to move the entire group of disks at the same time while confirming that they are all online and running on the destination computer before starting the import process. Moving dynamic disks with sensitive data is a delicate task and one should proceed with caution.

The following is a list of conversion possibilities using the Disk Management graphical snap-in:

  • Dynamic MBR can be converted to Dynamic GPT and vice-versa, if there are no volumes on the disk
  • Basic MBR can be converted to Basic GPT and vice-versa, if there are no volumes on the disk
  • Basic MBR can be converted to Dynamic MBR but the disk may become unbootable
  • Basic GPT can be converted to Dynamic GPT but the disk may become unbootable
  • Dynamic MBR can be converted to Basic MBR if there are no volumes on the disk
  • Dynamic GPT can be converted to Basic GPT if there are no volumes on the disk

If you are using the Diskpart command-line tool to convert dynamic disks between MBR and GPT, disks must be first converted to basic, then to MBR or GPT as appropriate and finally converted back to dynamic. In the graphical snap-in this step is done automatically in the background :)