Windows Server 2008 : Configuring Server Storage (part 2) - Managing Disks, Volumes, and Partitions

Managing Disks, Volumes, and Partitions in Windows Server 2008

The main tool you can use to manage disks, volumes, and partitions in Windows Server 2008 is Disk Management. With Disk Management, you can initialize disks, bring disks online or offline, create volumes within disks, format volumes, change disk partition styles, extend and shrink volumes, and create fault-tolerant disk sets.

To access Disk Management, you can type Diskmgmt.msc in the Run box, select Disk Management beneath the Storage node in Server Manager, or select the Disk Management node in the Computer Management console (accessible through Administrative Tools).

Disk Management is shown in Figure 5.

Figure 5. Disk Management in Windows Server 2008

Understanding Basic and Dynamic Disks

Disk Management enables you to manage both basic and dynamic disks.

By default, all disks are basic disks. A basic disk is a physical disk that contains primary partitions, extended partitions, or logical drives. The number of partitions you can create on a basic disk depends on the disk’s partition style. On disks that use the master boot record (MBR) partition style, you can create up to four primary partitions per basic disk, or you can create up to three primary partitions and one extended partition. Within the one extended partition, you can then create unlimited logical drives. On basic disks that use the GUID partition table (GPT) partition style, you can create up to 128 primary partitions. Because GPT disks do not limit you to four partitions, you do not need to create extended partitions or logical drives. GPT disks are recommended for disks larger than 2 terabytes (TB) and for disks on 64-bit systems.

Dynamic disks provide advanced features that basic disks do not, features such as the ability to create an unlimited number of volumes, volumes that span multiple disks (spanned and striped volumes), and fault-tolerant volumes (mirrored and RAID-5 volumes). There are five types of dynamic volumes: simple, spanned, striped, mirrored, and RAID-5.

In previous versions of Windows, you needed to convert a basic disk to a dynamic disk before you could create any of these volume types. When you use Disk Management in Windows Server 2008 to create any of these volume types, however, basic disks are automatically converted to dynamic during the process. As a result, the question of whether a disk is basic or dynamic has become less important from an administrative point of view. Despite this development, it is still important to know for dual-boot configurations that many earlier versions of Windows (such as Windows NT, Windows 98, and Windows ME) cannot access dynamic disks. Also relevant for dual-boot configurations is the fact that dynamic disks are compatible only with Windows operating systems.

Creating Volumes

You can use Disk Management or the Diskpart command-line utility to create the following volume types in Windows Server 2008.

• Simple or basic volumes Simple volumes are basic drives that are not fault tolerant. A simple volume can consist of a single region on a disk or multiple regions that are on the same disk and linked together.

  To create a simple volume in Disk Management, right-click unallocated space on a disk, and then click New Simple Volume, as shown in Figure 6. (This process is identical whether you are creating the volume on a basic or dynamic disk, even though on a basic disk, the new volume is technically called a partition or basic volume.) You might need to right-click the disk and select Online first.

  Figure 6. Creating a simple volume

  
  
  

  To create a simple volume by using the Diskpart utility, use the utility to select the disk and then, on a dynamic disk, type the command create volume simple. To create a new volume (partition) on a basic disk, type create partition. You can use create volume ? or create partition ? to learn the specific syntax associated with these commands.

• Spanned volumes A spanned volume is a dynamic volume consisting of disk space on more than one physical disk. If a simple volume is not a system volume or boot volume, you can extend it across additional disks to create a spanned volume, or you can create a new volume as a spanned volume by using unallocated space on more than one disk.

  To create a new spanned volume, in Disk Management, right-click unallocated space on one of the disks where you want to create the spanned volume, and then click New Spanned Volume. This step opens the New Spanned Volume Wizard, in which you can add space to the spanned volume from the disks available.

  Figure 7 shows a spanned volume, assigned drive letter E. Notice how the drive uses space from Disk 1 and Disk 2 but appears as only a single volume with a capacity of 7.32 GB.

  Figure 7. A spanned volume in Disk Management

  
  
  

• Striped volumes A striped volume, which is also known as RAID 0, is a dynamic volume that stores data in stripes across two or more physical disks. Striped volumes offer the best performance of all the volumes that are available in Windows, but they do not provide fault tolerance. If a disk in a striped volume fails, the data in the entire volume is lost.

  Figure 8 shows how data in a striped volume is written across a set of disks.

  Figure 8. A RAID 0 or striped volume stripes data across disks

  

  When should you use a striped volume? A striped volume is the best storage solution for temporary data that does not need fault tolerance but does require high performance. Examples of such temporary data include page files and Temp folders. To create a new striped volume in Disk Management, right-click unallocated space on a disk, and then click New Striped Volume.

  A striped volume in Disk Management is shown in Figure 9. Notice how the volume uses 1.46 GB of space from both Disk 1 and Disk 2 and appears as a single volume E with a total capacity of 2.93 GB. Note also how the volume is being used to store temporary data (the Page File).

  Figure 9. A Raid 0 Or Striped Volume In Disk Management

  
  
  

  Note: RAID disks

  As with all RAID solutions, a striped volume is built with disks of equal size.

  
  

• Mirrored volumes Also known as a RAID 1, a mirrored volume is a fault-tolerant volume that provides data redundancy by using two copies, or mirrors, of the same volume. All data written to the mirrored volume is written to both volumes, which are located on separate physical disks. If one of the physical disks fails, the data on the failed disk becomes unavailable, but the system continues to operate using the unaffected disk.

  Figure 10 illustrates how data is stored on a mirrored volume. Because data is duplicated, no data is lost if either disk fails.

  Figure 10. A RAID 1 or mirrored volume copies all data onto a second disk

  

  Note: Triple mirroring and beyond

  Although mirrored volumes configured in Windows Server 2008 are limited to two disks, mirrors created through third-party solutions can be created out of three disks or more. In a triple mirror configuration, for example, the contents of one disk are duplicated on two additional disks. Multiple mirrors degrade write performance but improve fault tolerance. They are good solutions for mission-critical data.

  
  

  As a fault tolerant solution, a mirrored volume has advantages and disadvantages. One advantage of a mirrored volume is that it offers very good read performance as well as fairly good write performance. In addition, mirroring requires only two disks, and almost any volume can be mirrored, including the system and boot volumes. The disadvantage of a mirrored volume is that it requires 50 percent of a disk’s total storage capacity to be reserved for fault tolerance. Overall, if you need a fault tolerant storage solution, a mirror is a good choice if you have only two disks; if you need good read and write performance; or if you need to provide fault tolerance for the system volume, the boot volume, or other mission-critical data.

  To create a mirrored volume, you can either add a mirror to an existing volume or create a new mirrored volume. To add a mirror to an existing volume in Disk Management, right-click the existing volume, and then click Add Mirror, as shown in Figure 11.

  Figure 11. Adding a mirror to the System partition

  
  
  

  To create a new mirrored volume in Disk Management, right-click unallocated space on a disk, and then click New Mirrored Volume. A new mirrored volume is shown in Figure 12. Notice how the drive uses 5.86 GB of space from both Disk 1 and Disk 2 and appears as a single volume E with a total capacity of 5.86 GB.

  Figure 12. A Raid 1 Or Mirrored Volume

  
  
  

• Raid-5 volumes A RAID-5 volume is a fault tolerant volume that combines areas of free space from at least three physical hard disks into one logical volume. RAID-5 volumes stripe data along with parity (evenness or oddness) information across a set of disks. When a single disk fails, Windows Server 2008 uses this parity information to re-create the data on the failed disk. RAID-5 volumes can accept the loss of only a single disk in the set.

Figure 13 shows a RAID-5 volume made up of four disks. Data written to the volume is striped across these disks from left to right. For each stripe across the set of disks, one disk is used to hold parity information about the evenness or oddness of the other data in the stripe. In the simplified example shown in Figure 2-13, parity is set to 1 when the sum of the values in the stripe is odd, and parity is set to 0 when the sum of the remaining values is even. Using this parity information along with other disk data, if any one (and only one) disk fails, Windows can reconstruct the complete contents of that failed disk. The data of the failed drive can be re-created in real time as users request it. The party information can also be re-created live on a new disk once the failed disk has been replaced.

Figure 13. A RAID-5 volume calculates parity (evenness or oddness) for fault tolerance

The space approximately equivalent of one disk is always used for fault tolerance in a RAID-5 volume. For example, if you create a RAID-5 out of four 120-GB disks, the total storage space available in that RAID-5 is 360 GB.

When should you use a RAID-5 volume? A RAID-5 volume is characterized by very good read performance, relatively poor write performance, and optimal use of storage space in a fault tolerant solution. Therefore, consider using a RAID-5 volume when good write performance is not a priority or when you need a fault tolerant storage solution that makes the best use of available storage. Note also that you cannot assign the system or boot partition to a RAID-5 volume created in Windows Server 2008.

To create a RAID-5 volume in Disk Management, right-click unallocated space on one of the dynamic disks on which you want to create the RAID-5 volume, and then click New RAID-5 Volume. Then, follow the instructions in the New RAID-5 Volume Wizard.

To create a RAID-5 volume by using the Diskpart utility, use the command create volume raid. You can use the help create volume raid command to learn the exact syntax.

Extending a Volume

You can add more space to existing simple or spanned volumes by extending them into unallocated space on the same disk or on a different disk. To extend a volume, it must either be formatted with the NTFS file system or unformatted. To extend a volume in Disk Management, right-click the simple or spanned volume you want to extend, and then click Extend Volume.

Note: Extending boot and system volumes

You cannot extend a boot or system volume onto another disk.

Shrinking a Volume

You can decrease the space used by simple or spanned volumes by shrinking them into contiguous free space at the end of the volume. For example, if you need to increase the amount of unallocated space on a disk to make room for a new partition or volume, you can attempt to shrink the existing volumes on the disk. When you shrink a partition, any ordinary files are automatically relocated on the disk to create the new unallocated space. There is no need to reformat the disk to shrink the partition.

The amount of space you can gain from shrinking a volume varies greatly. In general, the greater the percentage of unused space on the volume and the fewer the bad clusters, the more you will be able to shrink the volume. If, however, the number of bad clusters detected by dynamic bad-cluster remapping is too great, you will not be able to shrink the volume at all. If this occurs, consider moving the data and replacing the disk.

Caution: Do not shrink raw partitions that contain data

If a partition is not formatted with a file system but still contains data (such as a database file), shrinking the partition can actually destroy the data.

To shrink a volume in Disk Management, right-click the simple or spanned volume that you want to shrink, and then click Shrink Volume, as shown in Figure 14.

Figure 14. Shrinking a volume in Disk Management