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Disk Preparation
RAID

RAID stands for Redundant Array of Inexpensive (or Independent) Disks. RAID is a method of creating one or more pools of data storage space from several hard drives. It can offer fault tolerance and higher throughput levels than a single hard drive or group of independent hard drives.
RAID Array

RAID Provides real-time data recovery with uninterrupted access when a hard drive fails. As well as preventing data loss, it increases system uptime and availability. Performance increases can be obtained from multiple drives working in parallel.

Types of RAID

Software RAID Hardware RAID External RAID
Included in the OS such as Windows, Netware, and Linux. All RAID functions are handled by the CPU which can shag it out rather quickly for other jobs Processor-intensive RAID operations are offloaded from the CPU to enhance performance. Connects to the server via a standard controller. RAID functions are performed on a microprocessor located on the external RAID controller independent of the host.
Features Features Features
  • Low price
  • No special controller
  • Data protection and performance benefits
  • More robust fault-tolerant features and increased performance versus software-based RAID.
  • OS independent
  • Build super high-capacity storage systems for high-end servers.
  • RAID Levels

    RAID
    Level
    Minimum
    Number
    of Drives
    Description Strengths Weaknesses
    RAID 0 2 Data striping without  redundancy Highest performance No data protection; One drive fails, all data is lost
    RAID 1 2 Disk mirroring Very high performance; Very high data protection; Very minimal penalty on write performance High cost; Because  all data is duplicated, twice the storage capacity is required
    RAID 2 Not used in LAN No practical use Previously used for RAM error correction and in disk drives before the use of embedded error correction No practical use; Same performance can be achieved by RAID 3 at lower cost
    RAID 3 3 Byte-level data striping with dedicated parity drive Excellent performance for large, sequential data requests Not well-suited for transaction-oriented network applications; Single parity drive does not support multiple,  simultaneous read and write requests
    RAID 4 3 (Not widely used) Block-level data striping with dedicated parity drive Data striping supports multiple simultaneous read requests Write requests suffer from same single parity-drive bottleneck as RAID 3; RAID 5 offers equal data protection and better performance at same cost
    RAID 5 3 Block-level data striping with distributed parity Best cost/performance for transaction-oriented networks; Very high performance, very high data protection; Supports multiple simultaneous reads and writes; Can also be optimized for large, sequential requests Write performance is slower than RAID 0 or RAID 1
    RAID 0/1 4 Combination of RAID 0 (data striping) and RAID 1 (mirroring) Highest performance, highest data protection (can tolerate multiple drive failures) High cost; Because all data is duplicated, twice the storage capacity is required; Requires minimum of four drives
    RAID 1/0 4 Combination of RAID 1 (mirroring) and; RAID 0 (data striping) Shares the same fault tolerance as RAID 1 (the basic mirror), but compliments fault tolerance with a striping mechanism with higher read rates High cost; Because all data is duplicated, twice the storage capacity is required; Requires minimum of four drives


    Links

    RAID Types at Bytepile.com
    Cool RAID demo at Intel.com


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