RAID basics

What is RAID?

RAID stands for Redundant Array of Inexpensive Disks. Meaning that you can combine disks in different ways to create a large pool of space while protecting yourself from drive failures. Most RAID levels can survive the failure of at least one disk.

However, RAID is not a backup solution.

I'm going to say that again because it's important.

RAID is not a backup solution.

RAID only protects you from hardware failure. It doesn't save you from an errant rm -rf command. All the RAID in the world doesn't do you any good if all your files get deleted and you don't have backups somewhere else.

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RAID 0 combines a minimum of two disks into a single large disk. Two 100gb disks would give you 200gb of usable space. You can use disks of different sizes but you're limited by the size of the smallest disk.

Good

  • Fast read/write speeds

Bad

  • Lose one disk and you lose everything


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RAID 1 mirrors the contents of one disk onto another disk. Two 100gb disks would give you 100gb of usable space.

Good

  • Easy to set up. Most controller cards support it and it's pretty fast as software RAID.
  • Can easily handle a single drive failure and can sometimes handle multiple drive failures (depending on the total number of disks and the controller).

Bad

  • While read speeds are normal, writes are twice as slow
  • Not a very efficient use of available disk space.


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RAID 5 spreads parity data across all disks giving you more available storage with a comparable fault tolerance to RAID 1. This is a flexible and cost-effective option.

Good

  • Makes good use of disk space. That means four 100gb drives would providing 300gb of usable space under RAID 5 while only providing 200gb of usable space under RAID 1.
  • Very fast reads, medium-speed writes

Bad

  • Requires a minimum of 3 drives.
  • Rebuilding a failed array is much slower than RAID 1
  • Controller cards are more expensive


RAID 10 - Mirroring & Striping

RAID 10 is a great option if cost and hardware are not an issue and is achieved by taking two RAID 1 arrays and combining them into a RAID 0 array. Four 100gb drives would yield 200gb of usable space.

Good

  • Fault tolerance of RAID 1
  • Read/Write performance of RAID 0

Bad

  • Expensive to implement. Controller cards are generally pretty expensive and also requires a minimum of four disks.
  • Doesn't scale very well due to the sheer amount of hardware required.

Thanks to Wikipedia for the images. Don't worry, I'm not leeching them.