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2slow4u Escreveu:
Este artigo não me parece exactamente correcto, porque indica que o maior aumento de desempenho ocorre em RAID0, e na verdade o modo RAID1 oferece também um aumento de 2x relativamente a um disco só em transacções de leitura, além de ter a vantagem de que se um disco avariar, os dados ficam intactos no outro disco. Em modo RAID0, qualquer avaria num dos discos faz com que se perca toda a informação. Claro que com o RAID0 tem a vantagem de ter mais espaço utilizável, mas o aumento de desempenho ocorre tanto em RAID0 como em RAID1.
Depende tudo do valor que se dá à informação que se tem em disco...


Pedro Almeida Escreveu:o sistema raid tem de ser construido a partir de discos limpos, aos quais vamos pondo os ficheiros ou pode ser feito a partir de duiscos ja cheios???



(rād) Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employtwo or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.
There are number of different RAID levels:
# Level 0 -- Striped Disk Array without Fault Tolerance: Provides data striping (spreading out blocks of each file across multiple disk drives) but no redundancy. This improves performance but does not deliver fault tolerance. If one drive fails then all data in the array is lost.
# Level 1 -- Mirroring and Duplexing: Provides disk mirroring. Level 1 provides twice the read transaction rate of single disks and the same write transaction rate as single disks.
# Level 2 -- Error-Correcting Coding: Not a typical implementation and rarely used, Level 2 stripes data at the bit level rather than the block level.
# Level 3 -- Bit-Interleaved Parity: Provides byte-level striping with a dedicated parity disk. Level 3, which cannot service simultaneous multiple requests, also is rarely used.
# Level 4 -- Dedicated Parity Drive: A commonly used implementation of RAID, Level 4 provides block-level striping (like Level 0) with a parity disk. If a data disk fails, the parity data is used to create a replacement disk. A disadvantage to Level 4 is that the parity disk can create write bottlenecks.
# Level 5 -- Block Interleaved Distributed Parity: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. Level 5 is one of the most popular implementations of RAID.
# Level 6 -- Independent Data Disks with Double Parity: Provides block-level striping with parity data distributed across all disks.
# Level 0+1 – A Mirror of Stripes: Not one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1 mirror is created over them. Used for both replicating and sharing data among disks.
# Level 10 – A Stripe of Mirrors: Not one of the original RAID levels, multiple RAID 1 mirrors are created, and a RAID 0 stripe is created over these.
# Level 7: A trademark of Storage Computer Corporation that adds caching to Levels 3 or 4.
# RAID S: EMC Corporation's proprietary striped parity RAID system used in its Symmetrix storage systems.

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