# A CDE Definition

RAID 0

(

**R**edundant

**A**rray of

**I**ndependent

**D**isks Mode 0) A popular disk subsystem that increases performance by interleaving data across two or more drives. Data are broken into blocks, called "stripes," and alternately written to two or more drives simultaneously to increase speed. For example, stripe 1 is written to drive 1 at the same time stripe 2 is written to drive 2. Then stripes 3 and 4 are written to drives 1 and 2 simultaneously and so on. When reading, stripes 1 and 2 are read simultaneously; then stripes 3 and 4 and so on.

Ironically, RAID 0 is a misnomer because there is nothing "redundant." If one drive fails, the entire RAID array fails. See disk striping, RAID 3, RAID 5 and RAID.

**Disk Striping for Performance**

**RAID 0 Probability of Failure**

The more drives in a RAID 0 array, the higher the probability of array failure. For example, if experience tells us that one out of a thousand drives fails in a year, the probability that a 2-drive array will fail in a year is 1 in 500; that a 3-drive array will fail is 1 in 333 and so on.

The formula: if the probability of failure of each of n drives is p for a given period, then the probability of not failing is (1-p). The probability of all drives functioning is (1-p)^n, and the probability that at least one drive will fail, causing the array to fail, is [1-(1-p)^n].

**Before/After Your Search Term**

Before | After |
---|---|

RAID 1+0 | RAID1 |

RAID 10 | RAID10 |

RAID 3 | RAID3 |

RAID 4 | RAID4 |

RAID 5 | RAID5 |

RAID 6 | RAID6 |

RAID Advisory Board | rail |

RAID array | Rails |

RAID controller | Rain Doll algorithm |

RAID parity | Rainbow |

**Terms By Topic**

Click any of the following categories for a list of fundamental terms.