RAID (Redundant Array of Independent Disks) is a set of technology standards for teaming disk drives to improve fault tolerance and performance.
|2||Parallel Access with Specialized Disks|
|3||Synchronous Access with Dedicated Parity Disk|
|4||Independent Access with Dedicated Parity Disk|
|5||Independent Access with Distributed Parity|
|6||Independent Access with Double Parity|
Each RAID level represents a set of trade-offs between performance, redundancy, and cost.
RAID 0 uses striping to write data across multiple drives simultaneously. This means that when you write a 5GB file across 5 drives, 1GB of data is written to each drive. Parallel reading of data from multiple drives can have a significant positive impact on performance.
The trade-off with RAID 0 is that if one of those drives fail, all of your data is lost and you must restore from backup.
RAID 0 is an excellent choice for cache servers, where the actual data being stored is of little value, but performance is very important.
RAID 1 uses mirroring to write data to multiple drives. This means that when you write a file, the file is actually written to two disks. If one of the disks fails, you simply replace it and rebuild the mirror.
The tradeoff with RAID 1 is cost. With RAID 1, you must purchase double the amount of storage space that your data requires.
RAID 5 stripes data across multiple disks. RAID 5, however, adds a parity check bit to the data. This slightly reduces available disk capacity, but it also means that the RAID array continues to function if a single disk fails. In the event of a disk failure, you simply replace the failed disk and keep going.
The tradeoffs with RAID 5 are a small performance penalty in write operations and a slight decrease in usabable storage space.
RAID 0+1 combines the performance of RAID 0 with the redundancy of RAID 1.
To build a RAID 0+1 array, you first build a set of RAID 1 mirrored disks and you then combine these disk sets in a RAID 0 striped array.
A RAID 0+1 array can survive the loss of one disk from each mirrored pair. RAID 0+1 cannot survive the loss of two disks in the same mirrored pair.
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