Managing Windows Server 2012 Storage and File Systems : Storage Management (part 6) - Configuring storage - Using the MBR and GPT partition styles, Using the disk storage types

MBR uses a partition table that describes where the partitions are located on the disk. The first sector on a hard disk contains the MBR and a master boot code that’s used to boot the system. The MBR resides outside of partitioned space.

MBR disks support a maximum volume size of up to 4 TBs unless they’re dynamic disks and use RAID. MBR disks have two special types of partitions associated with them. The first partition type, called a primary partition, is used with drive sections that you want to access directly for file storage. You make a primary partition accessible to users by creating a file system on it and assigning it a drive letter or mount point. The second partition type, called an extended partition, is used when you want to divide a section of a disk into one or more logical units called logical drives. Here, you create the extended partition first, and then create the logical drives within it. You then create a file system on each logical drive and assign a drive letter or mount point.

Each MBR drive can have up to four primary partitions or three primary partitions and one extended partition. It is the extended partition that allows you to divide a drive into more than four parts.

GPT disks don’t have a single MBR. With GPT disks, critical partition data is stored in the individual partitions, and there are redundant primary and backup partition tables. Further, checksum fields are maintained to allow for error correction and to improve partition structure integrity.

GPT disks support partitions of up to 18 exabytes (EBs) in size and up to 128 partitions per disk. EFI-based computers using GPT disks for boot have two required partitions and one or more optional original equipment manufacturer (OEM) or data partitions. The required partitions are the EFI system partition (ESP) and the Microsoft Reserved (MSR) partition. Although the optional partitions that you see depend on the system configuration, the optional partition type you see the most is the primary partition. Primary partitions are used to store user data on GPT disks.

Keep in mind that additional GPT disks (data disks) do not require an ESP. Further, a basic GPT disk might not contain primary partitions. For example, when you install a new disk and configure it as a GPT disk, the Windows operating system automatically creates the ESP and MSR partitions, but it does not create primary partitions.

Although GPT offers a significant improvement over MBR, it does have limitations. You cannot use GPT with removable disks, disks that are direct-attached using USB or FireWire interfaces, or disks attached to shared storage devices on server clusters.

Tasks for using MBR and GPT disks are similar but not necessarily identical. Partitions and volumes on MBR and GPT disks can be formatted using FAT, FAT32, exFAT, NTFS, and ReFS. When you create partitions or volumes in Disk Management, you have the opportunity to format the disk and assign it a drive letter or mount point as part of the volume creation process. Although Disk Management lets you format the partitions and volumes on MBR disks using FAT, FAT32, exFAT, NTFS, and ReFS, you can format partitions and volumes on GPT disks using only NTFS or ReFS. If you want to format GPT disks by using FAT or FAT32, you must use the FORMAT command at the command prompt. Further, keep in mind that you can use Windows Server Backup to back up MBR and GPT disks and their volumes whether they are formatted with FAT, FAT32, exFAT, NTFS, or ReFS.

You can change partition table styles from MBR to GPT or from GPT to MBR. Changing partition table styles can be useful when you want to move disks between computers or you receive new disks that are formatted for the wrong partition table style. You can convert partition table styles only on empty disks, however. This means the disks must either be new or newly formatted. You could, of course, empty a disk by removing its partitions or volumes.

You can use both Disk Management and DiskPart to change the partition table style. To use Disk Management to change the partition style of an empty disk, start Computer Management from the Administrative Tools menu or by typing compmgmt.msc at the command line, expand the Storage node, and then select Disk Management. All available disks are displayed. Press and hold or right-click the disk to convert in the Graphical View, and then tap or click Convert To GPT Disk or Convert To MBR Disk as appropriate.

To use DiskPart to change the partition style of an empty disk, invoke DiskPart by typing diskpart and then selecting the disk you want to convert. For example, if you want to convert disk 3, type select disk 3. After you select the disk, you can convert it from MBR to GPT by typing convert gpt . To convert a disk from GPT to MBR, type convert mbr .

Basic disks use the same disk structure as early versions of the Windows operating system. When using basic disks, you are limited to creating four primary partitions per disk, or three primary partitions and one extended partition. Within an extended partition, you can create one or more logical drives. For ease of reference, primary partitions and logical drives on basic disks are known as basic volumes. Dynamic disks were introduced with early Windows operating systems as a way to improve disk support by requiring fewer restarts after disk configuration changes, improved support for combining disks, and enhanced fault tolerance using RAID configurations. All volumes on dynamic disks are known as dynamic volumes.

Windows Server 2012 systems can use both basic and dynamic disks. You cannot, however, mix disk types when working with volume sets. Note also that although you can continue to use dynamic disks with Windows 8 and Windows Server 2012, dynamic disks are being phased out in favor of Storage Spaces. If you want to mirror the volume that hosts the operating system, you might want to use dynamic disks because this is one of the best approaches. Otherwise, Microsoft recommends that you use Storage Spaces instead of dynamic disks.

All disks, regardless of whether they are basic or dynamic, have five special types of drive sections:

The volume types are set when you install the operating system. You can mark a partition as active to ensure that it is the one from which the computer starts. You can do this only for partitions on basic disks. You can’t mark an existing dynamic volume as the active volume, but you can convert a basic disk containing the active partition to a dynamic disk. After the update is complete, the partition becomes a simple volume that’s active.

Basic disks and dynamic disks are managed in different ways. For basic disks, you use primary and extended partitions. Extended partitions can contain logical drives. Dynamic disks allow you to combine disks to create spanned volumes, to mirror disks to create mirrored volumes, and to stripe disks using RAID 0 to create striped volumes. You can also create RAID-5 volumes for high reliability on dynamic disks.

You can change storage types from basic to dynamic and from dynamic to basic. When you convert a basic disk to a dynamic disk, existing partitions are changed to volumes of the appropriate type automatically and existing data is not lost. Converting a dynamic disk to a basic disk isn’t so easy and can’t be done without taking some drastic measures. You must delete the volumes on the dynamic disk before you can change the disk back to a basic disk. Deleting the volumes destroys all the information they contain, and the only way to get it back is to restore the data from backup.

You should consider a number of things when you want to change the storage type from basic to dynamic. To be converted successfully, an MBR disk must have 1 megabyte (MB) of free space at the end of the disk. This space is used for the dynamic disk database, which tracks volume information. Without this free space at the end of the disk, the conversion will fail. Because both Disk Management and DiskPart reserve this space automatically, primarily only if you used third-party disk management utilities will you need to be concerned about whether this space is available. However, if the disk was formatted using another version of the Windows operating system, this space might not be available either.

A GPT disk must have contiguous, recognized data partitions to be converted successfully. If the GPT disk contains partitions that the Windows operating system doesn’t recognize, such as those created by another operating system, you won’t be able to convert a basic disk to a dynamic disk.

You can’t convert a disk if the system or boot partition uses software RAID. You must stop using the software RAID before you convert the disk.

Both Disk Management and DiskPart can be used to change the storage type.

Using Disk Management to convert a basic disk to a dynamic disk To use Disk Management to convert a basic disk to a dynamic disk, start Computer Management from the Administrative Tools menu or by typing compmgmt.msc at the command line, expand the Storage node, and then select Disk Management. In Disk Management, press and hold or right-click a basic disk that you want to convert, either in Disk List view or in the left pane of Graphical View, and select Convert To Dynamic Disk.

In the Convert To Dynamic Disk dialog box (shown in Figure 12), select the disks you want to convert. If you’re converting a RAID volume, be sure to select all the basic disks in the set because they must be converted together. Tap or click OK when you’re ready to continue.

Next, as shown in Figure 13, the Disks To Convert dialog box shows the disks you’re converting along with details of the disk contents. To see the drive letters and mount points that are associated with a disk, select the disk in the Disks list and then tap or click Details. If a disk cannot be converted for some reason, the Will Convert column will show No and the Disk Contents column will provide a reason. You must correct whatever problem is noted before you can convert the disk.

When you’re ready to start the conversion, tap or click Convert. Disk Management will then warn you that after you finish the conversion you won’t be able to boot previous versions of the Windows operating system from volumes on the selected disks. Tap or click Yes to continue. If a selected drive contains the boot partition, system partition, or a partition in use, you’ll see another warning telling you that the computer will need to be rebooted to complete the conversion process.

Using DiskPart to Convert a basic disk to a dynamic disk To use DiskPart to convert a basic disk to a dynamic disk, invoke DiskPart by typing diskpart and then select the disk you want to convert. For example, if you want to convert disk 2, type select disk 2. After the disk is selected, you can convert it from basic to dynamic by typing convert dynamic.

Using Disk Management to change a dynamic disk back to a basic disk To use Disk Management to change a dynamic disk back to a basic disk, you must first delete all dynamic volumes on the disk. Then press and hold or right-click the disk, and select Convert To Basic Disk. This changes the dynamic disk to a basic disk, and you can then create new partitions and logical drives on the disk.

Using DiskPart to convert a dynamic disk to a basic disk To use DiskPart to convert a dynamic disk to a basic disk, invoke DiskPart by typing diskpart and then select the disk you want to convert. For example, if you want to convert disk 2, type select disk 2. If there are any existing volumes on the disk, you must delete them. You can do this by typing clean. However, be sure to move any data the disk contains to another disk prior to deleting the disk volumes.

After you delete all the volumes on the disk, you can convert the disk from dynamic to basic by typing convert basic. This changes the dynamic disk to a basic disk, and you can then create new partitions and logical drives on the disk.