Windows 7 : Managing Hard Disks - The Nature of Hard Disks,Windows 7 File and Storage Systems

1. The Nature of Hard Disks

For many users and system administrators, intelligent hard disk management forms the core of efficient system management. Until solid-state drive (SSD) technology becomes truly affordable, we’re stuck with the problems and limitations created by a crude system of motors, spinning platters, and delicate parts, such as read/write heads floating microns above a flying surface that can be easily ruined by particles as small as those found in a puff of cigarette smoke.

Perhaps someday, hard disks will be relics of the past, useful only for industrial art or bookends flanking tech books on a shelf. (They’ll make good doorstops, too.) Until that time, we’re stuck with the peculiar vagaries of hard disks. The good news is that high-capacity drives are cheap and plentiful.

No doubt the majority of Windows 7 users will never set up RAID arrays, multiple-booting arrangements, or dynamic disks; use encryption; or do any remote disk administration. Perhaps they will perform occasional disk cleanups and defragmenting, or learn to share folders over the network. These tasks are enough to get them by.

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2. Windows 7 File and Storage Systems

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.

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  A mirrored volume contains two disks; if either one fails, the OS goes to the other for data access. A RAID-5 volume contains three or more disks, any of which can fail without the system halting. The OS then reconstructs the missing data from the information contained on the remaining disks.

  
  

• 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.

  Caution

  Converting a hard disk to dynamic storage is a one-way process unless you use a third-party utility such as Partition Commander Professional 10. To change a dynamic disk back to a basic disk using the Windows 7 Disk Management tool, you must delete all volumes before converting the drive back to basic storage. Also note that dynamic disks can be read by Windows 7, Windows Vista, Windows XP Pro, Windows Server 2003, Windows Server 2008, and all versions of Windows 2000. Windows XP Home, Windows NT, Windows 98/SE/Me, and all earlier versions of Windows cannot access dynamic storage volumes. When you change the boot disk to dynamic, you can no longer multiboot into another OS because the familiar boot loader screen disappears. Only one installation of Windows can own a set of dynamic disks, so if you are planning to use dynamic disks as your RAID solution on a multiboot computer, think about investing in a hardware-based (SCSI or SATA) RAID solution.

  
  

• 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.