I do understand RAID 1. You have two drives that are mirrored. So when one drive fails, you have the full set of data on the other drive.
But with RAID 5 you are able to lose a complete drive out of a set of 3 for example. You have full data redundancy without sacrificing half of your capacity. How does this work?
In: 5
I’ll explain for storing 2 bits; the principle is the same in larger scale, just repeated a few billion times.
If you have 3 drives to store your 2 bits then you store 1 bit on the first drive and 1 on the second. This is how RAID 0 works, by the way. From there you want to store something on the 3rd drive that has information about both bits. If you were to just store another copy of the 1st bit, for example, then losing the 2nd drive would lose data.
The solution here is to store some notion of “the two bits are the same” or “the two bits are different.” Typically the convention is that if the bits are the same you store a 0 and if they’re different you store a 1.
In this setup if you lose the 3rd drive there’s no problem–all the original data was stored on the first two. If you lose the 1st or 2nd drive then you look at the 2nd or 1st to get one bit, then you look at the 3rd drive to figure out if the missing drive held the same bit or a different one.
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