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Extended Partitions

This is the part of a basic disk that contains a logical drive, which removes the restriction of four partitions per basic disk. Only one of the four basic disk partitions, though, can be extended. Note that extended partitions apply only to basic disks. For dynamic disks having no volume number limit, extended partitions are unnecessary.

Extent

A set of contiguous clusters storing a single file or part of a file. It is best to keep the number of extents for any file to a minimum as each extent requires a separate I/O operation. Reducing the number of extents in a file by the process known as defragmentation greatly improves performance.

Fault Tolerance

Basically, the computer is able to tolerate a fault of some kind, such as data loss or the failure of one disk. Despite such a hiccup, the system is able to continue without impacting the user community. Mirrored volumes or RAID-5 volumes must be created to add fault tolerance to a system.

File Allocation Table (FAT)

The part of the file system that keeps track of where data is stored on the disk. The three versions of the FAT file system are FAT12, FAT16, and FAT 32. The numbers used in these versions designate the number of bits used to identify a cluster.

Formatting

Putting the file structure on the disk.

Fragmentation

Allocation of noncontiguous sectors on a disk; that is, instead of placing a file in one location, parts of it are scattered all over the disk. Essentially, fragmentation means that files are broken into multiple pieces rather than residing in one contiguous block on a disk. When a fragmented file is opened, therefore, the head has to gather up all these pieces in order to display the file. Thus, the user experiences delays waiting for a document to appear. If the condition is in an advanced state (it is quite common for server files to be splintered into thousands of pieces), it might even take as long as 15 seconds to open a document that previously was available in one second.

Hard Quota

An enforceable quota limit on disk and directory usage, as set by an administrator. Changes in disk/directory usage are tracked; however, because quota limits are enforceable, the administrator is enabled to exert some control over user space consumption.

Head-Actuator Assembly

Consists of four principal components: read/write head, which is the part that takes the electronic 0s and 1s and converts them into the magnetic fields on the disk; actuator, which is the device that moves the arms containing the read/write heads across the platter surface; head arms, which move between the platters in order to store and access the data; and head slider, which is a block of material that holds the read/write head and acts as an airfoil to keep it positioned at the precise height above the surface of the platter.

Initializing (Partitioning)

Reserves a part of a disk for a certain function; the operating system considers each partition as a separate drive. Even if the entire disk is to be a single partition, that must be specified. When using dynamic disks in UNIX or Windows 2000, the term volume is used rather than partition.

Logic Board

Controls the disk rotational speed and directs the actuator in all its motions. To run the various components that comprise the modern hard drive, disk drives contain their own logic boards. Mounted on these boards are a microprocessor, memory chips, and many other more minor components.

Logical Cluster Number

The LCN refers to the location of the first cluster of each extent. Each file has a physical cluster number (PCN) and a logical cluster number (LCN). When no bad clusters are present, the PCNs and LCNs match exactly, but when the system discovers a PCN that is bad the LCN is directed to point to another PCN. Thus, two consecutive LCNs may be widely separated on the disk.

Logical Drives

Drives can also be grouped logically so that the operating system sees them as a single drive. For example, three physical 40-GB drives could be combined logically so that the operating system sees them all as a single 120-GB drive. Also, a physical drive may be partitioned into more than one logical drive.

Master File Table (MFT)

On NTFS, the MFT is a map of each and every file on the volume, and it is itself a file. Every time a new file is made, a new record in the MFT file is created. The MFT consists of a series of 1-KB records, one for each file in the partition.

Mean Time between Failures (MTBF)

The number of hours a disk can be expected to run, as reflected by the predicted failure rate in the first year; only useful as an enterprise metric. Divide the MTBF rating of disks by the number of disks in the enterprise for an approximation of how many disk failures can be expected during the first year.

MFT Zone

Because the MFT is such an important file, Microsoft reserved space for expansion on the disk immediately after the MFT called the MFT Zone. Approximately one eighth of an NTFS volume is reserved for the MFT Zone.

Microsoft Management Console (MMC)

An interface for the use of the different management snap-ins.

Mirrored Volume

A fault-tolerant volume for which the data is duplicated on two physical disks. All of the data on one volume is copied to another disk to provide data redundancy. If one of the disks fails, the data can still be accessed from the remaining disk. A mirrored volume cannot be extended. Mirroring is also known as RAID-1.

Mount Points

All Windows versions assign a different drive letter to each partition or volume on a disk, which limits the number of accessible volumes to the 26 letters of the alphabet. Mount points let the administrator attach other partitions to an empty directory within an already mounted NTFS volume. Rather than being limited to NTFS volumes, these additional volumes can also be using FAT16, FAT32, CD-ROM File System (CDFS), or Universal Disk Format (UDF), which expands the functionality of this feature.

Non-Catastrophic Failure

A subset of disaster recovery that encompasses various types of failure such as accidental deletion by a user, disk controller failure, hard disk drive crash, network downtime, or a power surge.

NTFS(New Technology File System)

A log-based file system that is more reliable and recoverable than early file systems. This is the file system used primarily on Windows 2000 and XP.

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