RAID is a data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. This was in contrast to the previous concept of reliable mainframe disk drives referred to as "single large expensive disk". Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of redundancy and performance; the different schemes, or data distribution layouts, are named by the word "RAID" followed by a number, for example RAID 0 or RAID 1. Each scheme, or RAID level, provides a different balance among the key goals: reliability, availability and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives; the term "RAID" was invented by David Patterson, Garth A. Gibson, Randy Katz at the University of California, Berkeley in 1987.
In their June 1988 paper "A Case for Redundant Arrays of Inexpensive Disks", presented at the SIGMOD conference, they argued that the top-performing mainframe disk drives of the time could be beaten on performance by an array of the inexpensive drives, developed for the growing personal computer market. Although failures would rise in proportion to the number of drives, by configuring for redundancy, the reliability of an array could far exceed that of any large single drive. Although not yet using that terminology, the technologies of the five levels of RAID named in the June 1988 paper were used in various products prior to the paper's publication, including the following: Mirroring was well established in the 1970s including, for example, Tandem NonStop Systems. In 1977, Norman Ken Ouchi at IBM filed a patent disclosing what was subsequently named RAID 4. Around 1983, DEC began. In 1986, Clark et al. at IBM filed a patent disclosing what was subsequently named RAID 5. Around 1988, the Thinking Machines' DataVault used error correction codes in an array of disk drives.
A similar approach was used in the early 1960s on the IBM 353. Industry manufacturers redefined the RAID acronym to stand for "Redundant Array of Independent Disks". Many RAID levels employ an error protection scheme called "parity", a used method in information technology to provide fault tolerance in a given set of data. Most use simple XOR, but RAID 6 uses two separate parities based on addition and multiplication in a particular Galois field or Reed–Solomon error correction. RAID can provide data security with solid-state drives without the expense of an all-SSD system. For example, a fast SSD can be mirrored with a mechanical drive. For this configuration to provide a significant speed advantage an appropriate controller is needed that uses the fast SSD for all read operations. Adaptec calls this "hybrid RAID". A number of standard schemes have evolved; these are called levels. There were five RAID levels, but many variations have evolved, including several nested levels and many non-standard levels.
RAID levels and their associated data formats are standardized by the Storage Networking Industry Association in the Common RAID Disk Drive Format standard: RAID 0 RAID 0 consists of striping, but no mirroring or parity. Compared to a spanned volume, the capacity of a RAID 0 volume is the same, but because striping distributes the contents of each file among all disks in the set, the failure of any disk causes all files, the entire RAID 0 volume, to be lost. A broken spanned volume at least preserves the files on the unfailing disks; the benefit of RAID 0 is that the throughput of read and write operations to any file is multiplied by the number of disks because, unlike spanned volumes and writes are done concurrently, the cost is complete vulnerability to drive failures. Indeed, the average failure rate is worse than that of an equivalent single non-RAID drive. RAID 1 RAID 1 consists of data mirroring, without striping. Data is written identically to two drives. Thus, any read request can be serviced by any drive in the set.
If a request is broadcast to every drive in the set, it can be serviced by the drive that accesses the data first, improving performance. Sustained read throughput, if the controller or software is optimized for it, approaches the sum of throughputs of every drive in the set, just as for RAID 0. Actual read throughput of most RAID. Write throughput is always slower because every drive must be updated, the slowest drive limits the write performance; the array continues to operate as long. RAID 2 RAID 2 consists of bit-level striping with dedicated Hamming-code parity. All disk spindle rotation is synchronized and data is striped such that each sequential bit is on a different drive. Hamming-code parity is stored on at least one parity drive; this level is of historical significance only. RAID 3 RAID 3 consists of byte-level striping with dedicated parity. All disk spindle rotation is synchronized and data is striped such that each sequential byte is on a different drive. Parity is calculated across correspond
Brightwood is an unincorporated community within the Mount Hood Corridor in Clackamas County, United States. It is located between Wemme and Sandy just off U. S. Route 26 at an elevation of 1165 feet, it is one of the communities. A post office called "Salmon" was established in the area in 1891, named after the nearby Salmon River; the post office was renamed Brightwood in 1910. The name Brightwood was said to have been coined by a local resident, Mr. Alcorn, for the pleasing effect of the sun shining on the cottonwood trees in the spring; this region experiences warm and dry summers, with no average monthly temperatures above 71.6 °F. According to the Köppen Climate Classification system, Brightwood has a warm-summer Mediterranean climate, abbreviated "Csb" on climate maps. Village Media related to Brightwood, Oregon at Wikimedia Commons
Garratt Lane is a long street in the London Borough of Wandsworth, part of the A217 road. It connects Wandsworth High Street to Tooting Broadway and is 4 kilometres long, it passes through Earlsfield and Summerstown, before their late 19th century development, fields of Wandsworth. Garratt Lane has mixed usage along its length. In the north it contains newly developed stores including a large single-storey shopping mall with parking above; the stretch between Allfarthing Lane and Burntwood Lane is diverse shophouses including a few professional services. The southern portion is residential, although around Summertown there are a few light industries and the Wimbledon Stadium; the southernmost part of Garratt Lane is unusual in. The original Garratt Lane was a narrower street than Garratt Terrace, the main connection to Tooting Broadway. Many people mistakenly called it Garratt Lane, so it was agreed to exchange the names; the south-east end of Garratt Lane, running from the junction with Fountain Road and Upper Tooting Road was called Defoe Road.
Most large public houses have survived along Garratt Lane, including The Old Sergeant and the Leather Bottle, both of which date to the 18th century. The latter figured in the mock Garrat Elections of the late 18th century, which were featured in the play The Mayor of Garratt by Samuel Foote. Garratt Lane is one of three major north–south routes in south-west Inner London, i.e. between the Lambeth/Southwark south bank areas and the gradual widening and receiving of local roads to the arterial A3, west of Wandsworth. The Lane follows a bank of the River Wandle so has quite a consistent rise as with the parallel A218 on the higher, western bank. Industries grew up in the 19th centuries along this east bank, which led to its prominence. A 1741 map of Rocque shows a road with a near identical orientation, which implies the road had early origins. A 1786 map shows and names Garratt Lane running on its present route; this map shows two lanes that intersect named: Half Farthing and Burnt Wood. The sub-settlement on its length was Wandsworth.
In 1803 the first commercial railway in Britain was opened along much of the northern section. This was the Surrey Iron Railway which connected the Thames at Wandsworth with these industries, those in Merton and Croydon. No sign remains of the railway, horse-drawn. Public transport in the form of horse buses was placed on the street in the latter part of the 19th century, in 1903 the London County Council extended and electrified the tramways; the trams started at the Thames near Westminster and went west and southwest on three route, one through Clapham Junction to Wandsworth, another through Brixton to Streatham, one through Balham to Wimbledon. The routes through Garratt Lane connected all three with the focal point being Tooting; when the London Passenger Transport Board was formed in 1933 to control all of London's transport, route 12 and route 30 ran the length of Garratt Lane. These routes were transformed to trolleybus routes in 1937. Again the mode of transport changed with buses replacing the trolleybuses.
This pattern of change occurred throughout London although now there is a tendency towards tramway existing in Croydon and proposed elsewhere. The railway crosses Garratt Lane at Earlsfield Station and the nearest Underground station is Tooting Broadway just opposite the south end of Garratt Lane. There are four listed properties on Garratt Lane: The Old Court House near Wandsworth High Street is set back from Garratt Lane by a small public garden, it held the Wandsworth Museum until 2008. St Andrews Church is in Earlsfield and is the Church of England parish church The Leather Bottle Public House, at Summers Green, has historic connections, it is documented as being in existence in 1745, but is older. Its appearance has changed little over the last 150 years. One of the engravings by Valentine Green, shows election of a Mayor of Garratt in front of the Leather Bottle. St Clement Danes Almshouses is known as Diprose Lodge, it is within a walled estate in Earlsfield. The Almshouses are now operated by the Borough of Merton.
"A History of London Transport" by T G Barker and M Robbins - published by George Allen and Unwin 1963 "The Times London Historic Atlas" edited by Hugh Clout - Published by The Times of London ISBN 0-7230-0342-4 "The Streets of London" by S Fairfield - published by Papermac ISBN 0-333-28649-9 "London Transport Tramways Handbook" by D W Willoughby & E K Oakley - published by the authors ISBN 0-903479-00-1 "A to Z of Victorian London" by Harry Margary, Lympne Castle, Kent