Redundant Array of Inexpensive Nodes
Encyclopedia
Reliable/redundant array of independent/inexpensive nodes (RAIN) is an architectural approach to computing and network-attached computer storage
(or NAS), that combines commodity or low-cost computing hardware
with management software to address the reliability and availability shortcomings of non-redundant NAS systems.
While RAID
protects data stored at the physical disk (or 'block') level, RAIN protects data stored at the file-system level, hence RAIN and RAID differ architecturally only in terms of the level of abstraction at which they are implemented.
Instead of storing multiple copies of the same data on physically separate hard disk
s on a server, data is replicated
to multiple servers. The software
that manages the array of RAIN servers knows where each copy is and, in the event of a server failure, can make additional copies (RAID-1 or 'mirroring') or use a parity-based RAID scheme (RAID-5 or similar) as necessary to keep an appropriate level of redundancy.
RAIN can also be used with tasks which require many instructions per second
to be processed. Instead of using a "tightly-coupled" computing cluster with specialized hardware
, arrays of inexpensive RAIN nodes can be assembled. The management software
transmits tasks to various computers and, in the event of a failure, will retry the task until a node responds. Many distributed computing
projects utilize, to some degree, a RAIN strategy.
Many of the distributed file sharing
services such as Gnutella
and eDonkey
are somewhat similar to RAIN systems, but they do not provide adequate redundancy by design—if none of the sharing users online have a copy of some part of a file, the file becomes inaccessible. A distributed hash table
is a better basis for implementing such a service, and the few large-scale distributed file system
s that exist are based on them (for example, the Chord
, Coral
, and Tahoe-LAFS projects).
Computer storage
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
(or NAS), that combines commodity or low-cost computing hardware
Hardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....
with management software to address the reliability and availability shortcomings of non-redundant NAS systems.
While RAID
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
protects data stored at the physical disk (or 'block') level, RAIN protects data stored at the file-system level, hence RAIN and RAID differ architecturally only in terms of the level of abstraction at which they are implemented.
Instead of storing multiple copies of the same data on physically separate hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
s on a server, data is replicated
Replication (computer science)
Replication is the process of sharing information so as to ensure consistency between redundant resources, such as software or hardware components, to improve reliability, fault-tolerance, or accessibility. It could be data replication if the same data is stored on multiple storage devices, or...
to multiple servers. The software
Computer software
Computer software, or just software, is a collection of computer programs and related data that provide the instructions for telling a computer what to do and how to do it....
that manages the array of RAIN servers knows where each copy is and, in the event of a server failure, can make additional copies (RAID-1 or 'mirroring') or use a parity-based RAID scheme (RAID-5 or similar) as necessary to keep an appropriate level of redundancy.
RAIN can also be used with tasks which require many instructions per second
Instructions per second
Instructions per second is a measure of a computer's processor speed. Many reported IPS values have represented "peak" execution rates on artificial instruction sequences with few branches, whereas realistic workloads typically lead to significantly lower IPS values...
to be processed. Instead of using a "tightly-coupled" computing cluster with specialized hardware
Hardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....
, arrays of inexpensive RAIN nodes can be assembled. The management software
Computer software
Computer software, or just software, is a collection of computer programs and related data that provide the instructions for telling a computer what to do and how to do it....
transmits tasks to various computers and, in the event of a failure, will retry the task until a node responds. Many distributed computing
Distributed computing
Distributed computing is a field of computer science that studies distributed systems. A distributed system consists of multiple autonomous computers that communicate through a computer network. The computers interact with each other in order to achieve a common goal...
projects utilize, to some degree, a RAIN strategy.
Many of the distributed file sharing
File sharing
File sharing is the practice of distributing or providing access to digitally stored information, such as computer programs, multimedia , documents, or electronic books. It may be implemented through a variety of ways...
services such as Gnutella
Gnutella
Gnutella is a large peer-to-peer network which, at the time of its creation, was the first decentralized peer-to-peer network of its kind, leading to other, later networks adopting the model...
and eDonkey
EDonkey network
The eDonkey network is a decentralized, mostly server-based, peer-to-peer file sharing network best suited to share big files among users, and to provide long term availability of files...
are somewhat similar to RAIN systems, but they do not provide adequate redundancy by design—if none of the sharing users online have a copy of some part of a file, the file becomes inaccessible. A distributed hash table
Distributed hash table
A distributed hash table is a class of a decentralized distributed system that provides a lookup service similar to a hash table; pairs are stored in a DHT, and any participating node can efficiently retrieve the value associated with a given key...
is a better basis for implementing such a service, and the few large-scale distributed file system
Distributed file system
Network file system may refer to:* A distributed file system, which is accessed over a computer network* Network File System , a specific brand of distributed file system...
s that exist are based on them (for example, the Chord
Chord project
In computing, Chord is a protocol and algorithm for a peer-to-peer distributed hash table. A distributed hash table stores key-value pairs by assigning keys to different computers ; a node will store the values for all the keys for which it is responsible...
, Coral
Coral Content Distribution Network
The Coral Content Distribution Network, sometimes called Coral Cache or Coral, is a free peer-to-peer content distribution network designed and operated by Michael Freedman...
, and Tahoe-LAFS projects).