So you'll have for example data here,

data here and you have the concept of parity information.

Now parity information allows you to rebuild the data if data is lost.

Now parity is calculated using a logical operator

known as XOR, okay.

Now, let me give you a very basic example of

how this operation works and how it can actually be applied to your data.

So with XOR if you take two bits of information,

and remember when data is stored in a disk it's stored as ones and zeros, right?

So if you compare two bits of information,

you run a sore operation to it,

if they're the same the parity value will be zero.

If they are different then the value will be one.

So if for whatever reason this information disappears,

all you have is this the fact that the parity value

zero you already know the data that is missing is zero.

Let's expand on this a little bit with the little more complicated bit of information.

Let's say for example 011, 110 like so.

So, if you were to calculate parity for this value,

so zero and one that's different,

one and one is the same,

one and zero is again different, so it's 101.

For whatever reason if this data disappears,

you can still figure out what this was originally by doing a comparison.

So one, zero that's one.

One and zero that's also a value of one.

Since they're the same,

remember if they're the same it's a zero.

It becomes a zero. So as you can see here the data comes back.

That is how you bring data back using your parity information.

So let's summarize.

So RAID is a storage technology that allows you to

speed up read and write access to your data,

it also provides fault tolerance.

Techniques that are applied to your data are striping,

which allows you to spread data across multiple disks.

Mirroring, which allows you to write your data in multiple locations,

identical data not information,

and if you use striping,

if you use parity information you can use your striped information to bring back

data from disks that have failed or have been removed.

Now with other RAID levels you will see a combination of striping,

mirroring, and parity, and they will be used in combination.

Thank you very much for

your time and I hope you will watch our future light-board sessions.