| array: |
|
the referent used to collectively indicate the entire group of physical drives being combined to form a single data storage resource; pertains to the second letter of the "RAID" acronym.
|
| availability: |
|
a state of stored data where all recorded information is fully and easily accessible; the name for the metric whose value is directly proportional to redundancy and is an indicator for the level of fault tolerance provided by a given RAID configuration.
|
| backup: |
|
a duplicate copy of file data made for protection against sudden loss of primary file data; a means of recreating lost computer file data.
|
| CDP: |
|
Continuous Data Protection; supercedes legacy data backup strategies; designed to eliminate protection gaps; can obviate the need for data recovery emergencies.
|
| controller: |
|
the electronic device organizing the overall RAID structure; on the "front" end, connects to the host system appearing as a single physical drive, on the "back" end, connects to each individual member hard disk drive in the array.
|
| degraded: |
|
the state of RAID operation when redundancy has been reduced or eliminated as an HDD member is taken off-line or disconnected from the array; takes place whenever an active HDD array member fails; e.g., one drive fails and RAID-5 becomes equivalent to RAID-0, or RAID-6 becomes equivalent to RAID-5.
|
| device: |
|
a computer hardware unit or instrument invented, designed, and produced to fulfill a particular function facilitating a specific purpose within a subsystem or other scheme for storage of data. |
| disk: |
|
see "drive" and "hard disk". |
| downtime: |
|
lost time or resource availability disruption caused by the cessation of computing system function when subsystem data are unavailable because the mass storage device(s) containing them are off-line or have failed; temporary, short duration loss may occur due to routine system maintenance or RAID array rebuild operations, while relatively long term disruption would follow when data without redundancy is lost, either temporarily or permanently. |
| drive: |
|
a unit, either physical or logical, serving as a repository for digital information, storing new or additional data up to its maximum capacity, and making this data accessible and retrievable on demand at any later time; an entire RAID subsystem may be referred to as. |
efficiency
(of storage capacity use): |
|
a value expressing the amount of available data storage capacity for stored information relative to the overall sum of storage capacity needed to implement a given level of RAID; formulaically expressed as "n+p", where "n" is the number of member drives needed to provide for the actual array capacity, and "p" is the number of member drives needed to provide additional capacity for redundancy, thus the larger the "n" value in proportion to the "p" value, the greater the efficiency. |
| element: |
|
a physical drive within an array; one of multiple identical data storage components, i.e., an HDD collectively constituting an array; usually synonymous with "member". |
fault tolerance
(loss protection factor): |
|
the degree to which a subsystem can withstand the failure of member components while maintaining data availability. |
| hard (disk) drive: |
|
HDD; a physical as opposed to a logical drive; magnetic digital data memory device using rotating disk platters as a magnetic medium for data recording. |
| host system: |
|
the computer processing system directly connected to, or in direct communication with the RAID controller for a given RAID data storage subsystem. |
| hot spare: |
|
any single HDD residing within a subsystem, and subject to automatic, ongoing confirmation of its operational status, but not being used to store data stripes, which can be automatically brought on-line by the RAID controller in the event of an array member HDD fault; an array member not active in storing any part of data currently stored on the subsystem array to which it belongs. |
| JBOD: |
|
Just a Bunch Of Disks; HDDs used collectively or independently and not configured as RAID. |
| layer: |
|
implementation of a data redundancy design feature capable of tolerating a single drive member failure while keeping all data stored on the subsystem available to the host system. |
| member: |
|
an HDD belonging to an array; usually synonymous with "element". |
| OS: |
|
Operating System; for the majority of the world's computer users, Windows® is the best known example; often referred to as the system platform; the entity serving as host to the file system. |
| protection gap: |
|
generally, the length of time between backup operations. |
| RAID: |
|
Redundant Array of Inexpensive Disks (the earliest known interpretation, the words "individual" and "independent" are often given nowadays for the "I" word); a data storage subsystem consisting typically of drives with data "striped" across the members of the array. Please see "View of RAID Types" and "Level/Type Definitions" for detailed information. |
| rebuild: |
|
a remedial operation performed following replacement of a failed RAID member drive to reestablish functional redundancy and nominal data availability. |
| redundancy: |
|
multiple means of data access within an array; in the event of array member drive fault, is the implementation of recording user information duplicates (via copies) or alternatively, means enabling the duplication of user information (via regeneration), thus protecting the RAID from data loss; is increased to provide greater data availability a given RAID subsystem; an increase of this decreases the storage efficiency; pertains to the initial letter of the "RAID" acronym. |
| restore, restoration: |
|
to bring inaccessible, unavailable, or otherwise off-line data back on-line; using objects of data protection to reinstate operation of stored data repository. |
| storage element: |
|
a device used to store data; see "element", and "member". |
| stripe: |
|
n.: a short, small segment of data that has been recorded upon any given drive element in a RAID. |
| striping: |
|
v.: the process of dividing a body of data into small, short segments and distributing the data segments sequentially across multiple members of a RAID drive or subsystem; contains no complete data file on any one drive (all elements need to be present). |
| subsystem: |
|
an entity subordinate to a host system; a pronoun for RAID. |
| Super RAID: |
|
a RAID design offering multiple layers of redundancy, or protecting against the concurrent failure of more than one data storage device or element; typically consisting of components, some or all of which are or could be stand-alone, single layer RAID configurations; see "Understanding RAID Levels". |
| uptime: |
|
a metric for high data availability; often expressed as a percentage of overall running time (e.g., 99.999% = "five nines"). |
| Z-end: |
|
the last, ending, concluding, terminating, closing, final, only remaining, entry of this MicroCom Glossary of RAID Terms. |
Compiled by: S.E. Fowler / Steve Fowler
