Raid is a system of using multiple hard disks as one unit. It breaks the data into chunks and distributes the data across the disks.
Raid 0 evenly sends the data across all disks without duplication. (without duplication means if one hard disk dies the you lose that data, and cannot be recovered). Raid 0 is the fastest as it can read disks simultaneously.
As an example:
Datastream: 1-2-3-4-5-6-7-8-9-..
Disk 1:1-3-5-7-9-..
Disk 2:2-4-6-8-...
RAID 1 duplicates the data between two or more disks. Losing one disk leaves a backup on the second (or third...) disk
As an example:
Datastream: 1-2-3-4-5-6-7-8-9-..
Disk 1:1-2-3-4-5-6-7-8-9-..
Disk 2:1-2-3-4-5-6-7-8-9-..
Downside is it is space-inefficient. To store 80Gb of data you need two or more hard disks each 80Gb or larger.
Raid 5 is a distributed duplication system, which is a little harder to explain.
Step1/ Get the data.
(example datastream:1-2-3-4-5-6-7-8-9-..)
2/ Create parity data chunks for the data
(example: 1-2-3-p1-4-5-6-p2-7-8-9-p3-...)
3/ Write to disks.
Datastream:1-2-3-p1-4-5-6-p2-7-8-9-p3-...
Disk 1:1-5-9-....
Disk 2:2-6-p3-...
Disk 3:3-p2-8-...
Disk 4:4-p1-7-...
Summary:
Raid 0: fastest, no backup, most efficient storage. Needs at least 2 disks.
Raid 1: Relatively fast, good backup, least efficient storage. Needs at least 2 disks.
Raid 5: somewhat fast(often slow write speed), reasonable backup, reasonably efficient storage. Needs at least 3 disks.
