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You have selected free tutorial of the Microsoft Corporation for the Microsoft Technology Associate (MTA) :
98-349: MTA: Windows Operating System Fundamentals : Module 5: Managing Devices :
Understanding Storage Device Types
Microsoft Help:-
Windows 7 supports two types of storage models: basic disks and dynamic storage. Windows 2000,
Windows XP Professional, and Windows Vista also support dynamic storage. When you prepare a
hard disk for use, you can choose between these storage models. The following sections explain
how they differ and when to use each type.
Basic Disks
The traditional storage model of disk structure uses partition tables. Each hard drive can hold up to
four primary partitions or up to three primary partitions and one extended (secondary) partition.
Within this extended partition, you can create logical drives. The total number of primary partitions
and logical drives cannot exceed 32 per hard drive. This disk structure is understood and can be
accessed by MS-DOS, all versions of Windows NT, as well as
Windows 2000, XP, Vista, and Windows 7. When viewed in
Disk Management, a disk drive prepared in this fashion is
known as a basic disk.
The annoyances and limitations of this partition table methodology
are artifacts of Microsoft operating systems, incidentally,
not something imposed by hard disks themselves or their
manufacturers. Some other OSs don’t suffer the same peculiarities.
The major reasons to continue using basic storage include
• Support for all versions of Windows that can read the file
system used on the drives. For example, if you need to
support dual-booting with Windows XP Home Edition and
Windows 7, you must use a file system that both OSs support. XP Home does not support
dynamic disks, so you must use basic disks.
• Support for multiboot configurations. Dynamic disks don’t
use boot loaders, so you cannot select between OSs; therefore,
you cannot use this type of storage as your only drive
in a multiboot configuration.
You can convert basic to dynamic disks without data loss, but
to convert a dynamic disk back to a basic disk using the
Windows 7 Disk Management tool, you must delete the disk
structure (and, of course, the data).
Dynamic Storage
With dynamic storage, the restraints of primary and extended partitions are gone. Under this storage
model, free space on a hard drive is divided into volumes instead of partitions; these volumes
can be noncontiguous and can span one or more disks. In addition, volumes on a dynamic disk can be configured as simple, spanned, mirrored, striped, or RAID-5,
as described next. Basic storage partitions can be configured
only as simple partitions, unless they are remnants from a previous
OS retained during an upgrade.
- Simple volume—Uses free space available on a single disk.
This space can be a single contiguous region or multiple
concatenated regions. Under the basic storage model, each
partition or logical drive is assigned a separate and distinct
drive letter, and functions as a distinct region of disk space.
Dynamic storage can be configured to see multiple regions
of a disk as a single volume, accessed with a single assigned
drive letter.
- Spanned volume—Extends the concept of a simple volume
across multiple disks (up to a maximum of 32). All joined
regions on these disks are seen as a single volume to programs
accessing them. However, if a single unit in a
spanned volume fails, the entire set is lost.
- Mirrored volume—A volume in which data from one disk is
mirrored or duplicated on a second disk. This process provides
for data redundancy, often called fault tolerance. If one
disk fails, the data can be accessed from the second disk. A
mirrored volume cannot be spanned; each volume must be
contained on a single disk. Programs see only one volume,
and Windows ensures that both disks are kept in sync.
Mirroring is also known as RAID-1.
- Striped volume—A volume in which data is stored across
two or more physical disks. When data is written to a striped
volume space, it is allocated alternately and evenly to each
of the physical disks. A striped volume cannot be mirrored or
spanned via Windows 7. (It is possible on hardware-based
RAID.) Striping, often termed RAID-0, is used to increase
storage system throughput. If a single unit in a striped volume
fails, the entire set is lost.
- RAID-5 volume—A fault-tolerant version of a striped
volume. When data is written to a RAID-5 volume, it is
striped across an array of three or more disks, and a parity
value is added. If a hard disk belonging to a RAID-5 volume
fails, the remaining drives can re-create the data using this
parity value. Note the difference here between a mirrored
volume and a RAID-5 volume. What are the advantages of dynamic storage?
- First and foremost, noncontiguous regions of multiple disks can be linked so that they appear as
one large region of disk space to any program. By linking them, you can increase the size of a
disk volume on-the-fly, without reformatting or having to deal with multiple drive letters.
- Second, and perhaps more important, from an administrator’s point of view, disk and volume
management can be performed without restarting the OS.
However, on a multiboot system, OSs other than Windows 7, Windows Vista, Windows 2000 (Server
and Professional), Windows XP Professional, Windows Server 2003, and Windows Server 2008 cannot
see dynamic storage drives. Unlike NTFS, which applies to only the formatted partition, dynamic
storage affects the entire hard drive. So if you plan to use dynamic storage, plan ahead and keep
other OSs on different hard drives. In addition, you must ensure that the boot drive is a basic storage
drive so that the boot menu will function.
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