RAID Explanation covering JBOD and RAID Levels 0, 1, 5 and 6

The first level of RAID is RAID 0, commonly referred to as striped RAID. This level of RAID is only for users looking for speed. RAID 0 requires at least two drives. RAID 0 is very dangerous for users looking for reliability. If one disk in the RAID array dies the whole array is trashed. Generally the more disks in the array the faster read and write times will be, but the greater the chance of the array failing. The size of a RAID 0 array is the size of all the drives in the array combined.

RAID 1, also know as mirrored RAID will increase data integrity, but requires two drives of the same size. RAID 1 makes an exact copy of a hard drive therefore using 50% of the total storage for redundancy. For example, if a user has two 500GB hard drives making their array 1TB they will have 500GB of actual storage. In most RAID setups, RAID 1 will increase the the read speed but will slightly decrease the write speed.

RAID 5 is my favorite level of RAID for secure storage of files. RAID 5 requires at least 3 drives to operate and will continue to work even in the event of a drive failure. RAID 5 is more efficient than RAID 1 when it comes to data storage. RAID 5 uses just ^one disk in the array for redundancy. So the more drives in the array the more efficient the array becomes. For example, if a user had three 500 GB hard drives totaling 1.5 TB and they were using RAID 5 they would have about 1 TB of actual storage. This makes RAID 5 much more efficient than RAID 1. RAID five has slower write speeds than RAID 1 or a standalone drive, but read speeds are often increased.

^ Note: this is inaccurate.  RAID5 uses all discs in the array for redundancy, but does so in a more efficient way than RAID mirroring does, such that with RAID5, about (n-1) of the drives' worth of space can be actual data.  If you want a RAID system that really does use one actual disc to store your redundancy data on, then you need RAID 4.

RAID 6 is almost the same as RAID 5 but it can sustain 2 drives losses instead of 1. RAID 6 requires at least 4 drives to operate and will continue to work even if two drives are missing. RAID 6 is best used for mission critical applications. The greater the total number of drives the more efficient the array becomes. Storage can be calculated by adding up the total number of drives in the array and subtracting two drives. For example, if there are four 500GB drives in the array there would be 1TB of available storage.

JBOD isn't an official RAID setup (because it's not a redundant array of any kind), but most RAID setups offer it as an option. A JBOD array basically takes a bunch of disks and turns them into one big partition. JBOD offers no redundancy and with some RAID setups, the failure of one disk in the array will cause the whole JBOD array to fail. Unlike RAID 0, a JBOD array reads and writes at the same speed as a normal disk.