What is the difference between raid 5 and raid 6 which one is better and why?

Answer 1

Neither is better, but each has a trade-off against the other. RAID is designed, basically, to use multiple hard drives in an "array" and use the array to protect you against lost data. What happens is that, when your computer is "writing" information to a disk, the data will be broken down into "chunks" called "stripes." The stripes are then distributed to the hard drives for safe keeping, and it also leaves itself a special key called a "parity stripe." What is special about the "parity stripes" is that they can be used to figure out what all the other stripes are.

Why this is helpful

In RAID 5, the equivalent of one hard disk will be dedicated to saving those special parity stripes and it spreads them across all the disks, so in the event that one of the drives fails, the computer can use the parity stripes to reconstruct whatever data was missing so the drives in the array can keep functioning. A RAID 5 array can survive the failure of up to one drive. Once one drive fails, you must replace the drive to fix the array because if two drives fail, the array can be ruined and you may lose the data.

Though this gets a little tricky, it's helpful to explain that RAID 5 uses the equivalent of one hard drive to store the parity stripes but, as mentioned above, it spreads them out over all disks. So, let's say you had 5 Hard drives, and each one was 1 terabyte (1000 gigabytes). Imagine that RAID 5 uses 20% of drive 1, 20% of drive 2 and so on so that between all 5 drives, there is a total of 1 terabyte available for storing those crucial parity stripes.

This means that, if you got a computer with five, 1 terabyte hard drives you wouldn't actually be able to save 5 terabytes of information on them because the computer is reserving at least 1 terabyte for itself (to store the parity stripes).

It's important to understand this to understand RAID 6.

The trade offs of RAID 6

RAID 6 is for those who want to trade off a little more of their storage space in order to completely maximize their data safety. It's very simple: instead of using the equivalent of 1 hard drive like RAID 5, RAID 6 uses two. Going to the analogy above, instead of using 20% of 5 drives to store those parity stripes in your machine, it would use 40%. The trade-off is that now you have even less room in RAID 6 to store your own information (because the computer is saving more for its parity stripes) but in the event of a drive failure, the RAID 6 can withstand double the failures that RAID 5 can.

To recap:

RAID 5- you have five, 1 terabyte hard drives and you can use 4 terabytes for yourself, 1 is saved for parity. If a drive fails? No problem, just repair the drive. If another drive fails before you repair? Your array comes down.

RAID 6- your same five, 1 terabyte hard drives now only have 3 terabytes available for you to store information on because it's using double space for parity. But if a drive fails, and before you can repair it, another drive fails? No problem, double the safety. The array stays up.