Data Availability

Expressed as Mean Time to (Loss of ) Data Availability (MTDA-q.v.). The length of expected continuous span of time over which applications can access correct data stored by a population of identical disk systems in a timely manner.

Data Reliability

Expressed as Mean Time to Data Loss (MTDL-q.v.). The length of the expected continuous span of time over which data stored by a population of identical disk systems can be correctly retrieved

Data Transfer Rate

The amount of data per unit time moved through a channel or I/O bus in the course of execution of an I/O load. For disk system I/O, data transfer capacity is usually expressed in Mbytes/second (millions of bytes per second.) cf. data transfer capacity

Device

A storage device (q.v.).

Disk

A non-volatile, randomly addressable, re-writable data storage device. This definition includes both rotating magnetic and optical disks and solid-state disks, or non-volatile electronic storage elements. If does not include specialized devices such as write-once-read-many (WORM) optical disks, nor does it include so-called RAM disks implemented using software to control a dedicated portion of a host computer!|s volatile random access memory.

Disk Array

A collection of disks form one or more commonly accessible disk systems, combined with an Array Management Function (q.v.). The Array Management Function controls the disks!| operation and presents their storage capacity to hosts as one or more virtual disks. The ANSI X3T10 committee refers to the Array Management Function as a storage array conversion layer (SACL). The committee does not have an equivalent of the term disk array in the sense in which it is used by the RAID Advisory Board.

Disk Block

The unit in which data is stored and retrieved on a fixed-block architecture (q.v.) disk. Disk blocks are of fixed usable size (with the most common being 512 bytes), and are numbered consecutively. Disk blocks are also the unit of data protection; whatever mechanism a disk employs to protect against data errors protects blocks of data.

Disk Striping

A disk array data mapping technique in which fixed-size sequences of virtual disk data addresses are mapped to sequences of member disk addresses in a regular rotating pattern. Disk striping is commonly called RAID Level 0 because of its similarity to common RAID data mapping techniques. Disk striping includes no data protection, however.

Driver, Driver Software

An I/O driver.