Implementing Disk Management in Windows Server 2008
Understanding Disk Terminology
Overview of Disk Management
Partitions and Volumes
Setting Disk Quotas
Enabling File Encryption
Servers are used for many functions and have many reasons for existence, but the single most pervasive function of most servers is storage. And you can’t store anything if you don’t have something to store it on. For servers, that something is primarily hard disks. Rather than cover all topics related to storage in a single chapter, we’ve split it up a bit. Both for reasons of length (our editors have this irrational fear of 100+ pages chapters) and also to group topics together rationally.
In this chapter, we’ll start by defining some terms that we’ll use throughout our discussions of storage. Once we’ve got that basic ground covered, we’ll move on to the physical aspects of storage—the disk subsystem and how you manage and administer it. This includes disks, partitions, and volumes, along with logical drives. And we’ll cover special features of the NTFS file system, including encryption and quotas. Throughout this chapter, we’ll cover both the graphical way to do things and the command-line way.
In Chapter 20, “Managing Storage,” we’ll shift gears and talk about storage from a logical perspective, with full coverage of the Storage Resource Manager, and we’ll also cover Storage Area Networks (SANs)—a way to centralize and abstract storage for a group of servers.
The hard disk management functions of Windows Server 2008 build on earlier versions of Windows Server to make hard disk management flexible and easy for administrators while hiding the complexities from end users. One important—and long overdue—new feature is the ability to grow or shrink partitions dynamically without losing data.
Understanding Disk Terminology
Before going into the details of managing disks and storage, let’s review some definitions:
Physical drive The actual hard disk itself, including the case, electronics, platters, and all that stuff. This is not terribly important to the disk administrator.
Partition A portion of the hard disk. In many cases, this is the entire hard disk space, but it needn’t be.
Allocation unit The smallest unit of managed disk space on a hard disk or logical volume. It’s also called a cluster.
Primary partition A portion of the hard disk that’s been marked as a potentially bootable logical drive by an operating system. MS-DOS can support only a single primary partition, but Windows Server 2008 can support multiple ones. There can be only four primary partitions on any hard disk.
Extended partition A nonbootable portion of the hard disk that can be subdivided into logical drives. There can be only a single extended partition per hard disk, but it can be divided into multiple logical drives.
Extended volume Similar to, and sometimes synonymous with, a spanned volume. This is any dynamic volume that has been extended to make it larger than its original size. When an extended volume uses portions of more than one physical disk, it is more properly referred to as a spanned volume.
Logical drive A section or partition of a hard disk that acts as a single unit. An extended partition can be divided, for example, into multiple logical drives.
Logical volume Another name for a logical drive.
Basic disk A traditional disk drive that is divided into one or more partitions, with a logical drive in the primary partition, if present, and one or more logical drives in any extended partitions. Basic disks do not support the more advanced functions of Disk Management, but they can be converted to dynamic disks in many cases.
Dynamic disk A managed hard disk that can be used to create various volumes.
Volume A unit of disk space composed of one or more sections of one or more disks. Prior versions of Windows Server used volume only when referring to dynamic disks, but Windows Server 2008 uses it to mean partitions as well.
Simple volume Used interchangeably with partition in Windows Server 2008, earlier versions of Windows used simple volume only when referring to a dynamic disk. A portion of a single disk, a simple volume can be assigned either a single drive letter or no drive letter and can be attached (mounted) on zero or more mount points.
RAID (redundant array of independent [formerly “inexpensive"] disks) The use of multiple hard disks in an array to provide for larger volume size, fault tolerance, and increased performance. RAID comes in different levels, such as RAID-0, RAID-1, RAID-5, and so forth. Higher numbers don’t necessarily indicate greater performance or fault tolerance, just different methods of doing the job.
Spanned volume A collection of portions of hard disks combined into a single addressable unit. A spanned volume is formatted like a single drive and can have a drive letter assigned to it, but it will span multiple physical drives. A spanned volume—occasionally referred to as an extended volume—provides no fault tolerance and increases your exposure to failure, but does permit you to make more efficient use of the available hard disk space.
Striped volume Like a spanned volume, a striped volume combines multiple hard disk portions into a single entity. A striped volume uses special formatting to write to each of the portions equally in a stripe to increase performance. A striped volume provides no fault tolerance and actually increases your exposure to failure, but it is faster than either a spanned volume or a single drive. A stripe set is often referred to as RAID-0, although this is a misnomer because plain striping includes no redundancy.
Mirror volume A pair of dynamic volumes that contain identical data and appear to the world as a single entity. Disk mirroring can use two drives on the same hard disk controller or use separate controllers, in which case it is sometimes referred to as duplexing. In case of failure on the part of either drive, the other hard disk can be split off so that it continues to provide complete access to the data stored on the drive, providing a high degree of fault tolerance. This technique is called RAID-1.
RAID-5 volume Like a striped volume, a RAID-5 volume combines portions of multiple hard disks into a single entity with data written across all portions equally. However, it also writes parity information for each stripe onto a different portion, providing the ability to recover in the case of a single drive failure. A RAID-5 volume provides excellent throughput for read operations, but it is substantially slower than all other available options for write operations.
SLED (single large expensive disk) Now rarely used, this strategy is the opposite of the RAID strategy. Rather than using several inexpensive hard disks and providing fault tolerance through redundancy, you buy the best hard disk you can and bet your entire network on it. If this doesn’t sound like a good idea to you, you’re right. It’s not.
JBOD Just a bunch of disks. The hardware equivalent of a spanned volume, this has all the failings of any spanning scheme. The failure of any one disk will result in catastrophic data failure.