- [Instructor] There are many types of RAID
as shown by the myriad versions available,
RAID zero, RAID one, five, six, one plus zero,
and on and on and on.
You rarely see two through four.
Those are parity types of RAID that have been completely
eclipsed by five and six so you rarely see those.
And while they are all redundant,
not all are truly fault tolerant.
Redundant means that you have more than one.
Fault tolerant means that you can survive a failure
and still get access to your data.
And that's what you want.
For example, RAID zero is not fault tolerant.
RAID zero is just known as striping.
You Stripe data across multiple drives
to increase speed and performance.
So we don't really use RAID zero
if we want something fault tolerant,
because if one drive was to fail,
we would lose all of the data.
Instead, we'll go for RAID types such as RAID one,
which is mirroring and RAID five which
is striping with parity.
These are very common types of fault tolerant RAID.
They can survive a fault or a failure
and keep supplying data to the users.
Let's describe those two in a little detail now.
RAID one is known as mirroring.
It requires two drives which should be
of the same make and model.
For example, you would want the same Western digital drives,
within the same blue series.
All data is written to both of the drives.
It's mirrored.
If one drive fails, then the other continues
to function offering that fault tolerance that you want.
Data is normally read from only one drive.
So in that respect, you get the same performance
as you would in a single drive system,
but when you write the data to the mirror,
it takes a little longer 'cause you're writing
to two drives at the same time.
Let's show an illustration of this.
Here, we have two discs, disc one and disc two each
of which are 500 gigabytes and they're connected
to a RAID controller.
And quite often the controller is just an adapter card,
could be a PCI express by one card
or it could be an integrated device within your motherboard.
When the mirror is created, the two drives
basically become one.
They're collectively known as a single volume letter.
In this case, we chose M, M for mirror,
but you can choose whatever letter you want
as long as it's not been used yet.
One of the issues you might find with RAID one arrays,
is that the controller acts as a single point of failure.
And so you could create a new configuration where each disc
is connected to a separate controller.
And this is known as disc duplexing.
So you have even more fault tolerance at this point
RAID arrays can be controlled through hardware
or through software.
An example of hardware would be using a RAID adapter card
as we mentioned before, where a RAID enabled motherboard
and the array is created within the card
or the motherboard's firmware.
This is done outside of the operating system.
An example of software would be to create
the array in compliant versions of Windows,
say within the disc management console Window.
Let's show an actual RAID one array
that was created within Windows
and then we'll show one that's created
in firmware on a separate system.
Here's an example of a RAID one array controlled
by software in Windows.
And it's controlled within the disc
management console Window.
Here, we have our list of volumes, for example,
the C volume which is on its own hard drive.
And that's where the operating system lives.
And then we have the M volume which is the mirror
and that is comprised of two other discs,
disc two and disc three.
And you can see here, the reddish brown header,
indicates a mirrored volume.
So M is the mirrored volume.
Any data that is written to this volume is written
to both drives simultaneously.
When it's read from the volume,
it just reads from the first volume in the mirror, disc two.
If one disc was to fail and most likely
that's the lower number in the mirror,
disc two would probably be the first to fail,
but if that was to fail, then the mirror would be broken.
However, users would still be able to read
and write data from disc three.
The M volume would continue to function
and that is the fault tolerant portion of RAID one,
but we would need to fix it.
We'd need to replace that disc two physically
and then rebuild the mirror which would then copy all
the data from disc three to disc two
and then it would resynchronize
and then we would have our mirror back.
Now, here's an example of a RAID one array
controlled by firmware.
This is Intel Rapid Storage Technology.
It's a built in RAID controller within the motherboard.
This motherboard can handle RAID one and can do RAID five.
In this case, I have a RAID one array.
There's two Western digital drives working in concert.
Each one is one terabyte that shows up here
as 931 gigabytes.
And it shows you that it is indeed a RAID one mirror.
If this mirror was to break, if it was to fail,
we would have to fix it here.
We would have to do recovery here and not in Windows.
If we were to take a look at the volume that was created
for this RAID one mirror in Windows in disc management,
we would see it would just be one drive.
It would show up as one disc, not as two
as you can see here.
And this is the disc management Window again.
Data E is that mirror, but it only shows as one disc.
So you don't actually know that you have a
mirror running here.
If you look at it from Windows,
you would have to look at the discs individually
within the BIOS or within the firmware.
And again, if it was to fail, you'd have
to rebuild it within the firmware itself.
And to get into that firmware for Intel,
it's usually Control + I, and you press
that before you would even get into the BIOS.
Your F2 to get into an Intel BIOS.
You press the Control + I to get into the firmware
for the RAID adapter before that.
And that's again, Control + I.
So that's RAID one.
Now, we move into RAID five, which is known
as striping with parity.
With RAID zero, you Stripe data across multiple drives
to increase performance.
And you do this with RAID five as well,
but now we also use parity so that in the event
of data failure we can use the parity information
to recreate that data.
It requires a minimum of three drives,
which should be of the same make and model.
RAID five arrays often have three, four or five drives,
but you're not limited to that.
I believe the normal maximum for hardware
and software is 32 drives.
Data is striped across all drives regardless
of how many drives you have.
Again, it's done in an effort to increase performance.
Parity information is distributed across drives
in a staggered format.
This is known as distributed parity blocks.
Any block of data also has a calculated amount
of parity and that's for repairing the data
if that particular drive fails.
This parity information is distributed among all
the other drives, except for the one where
the data was written to.
So in this scenario, the data is divided into three parts,
A, B and C.
Let's imagine that we have a 384 kilobyte file
that we want to write to the array.
Well, that's going to be written in blocks
to each drive one at a time.
And each of these blocks would be 64 kilobytes.
So for example, drive one and drive two will be written to
and A1 is a 64 kilobyte block.
A2 is another 64 kilobyte block.
And these are also sometimes referred to as chunks.
Together, they are a Stripe of data.
And it continues in that manner.
The next 64 kilobyte block would be B1 and B2,
but this time they're written to drive one and drive three.
And then the C block of data, C1 and C2 which are written
to drive two and drive three.
In total, we have six blocks of data.
And if you multiply that by 64 kilobytes each,
that gives us our total of 384 kilobytes,
which is the size of the file.
The parity for each Stripe of data
is placed on the remaining drive.
Now, in an effort to protect the data in the event
of failure, we're using this parity.
So parity for each Stripe of data is placed
on that remaining drive for each letter,
for each set of blocks, basically.
And you can think of parity information as a sort
of compressed version of the Stripe of data.
So the A1 and A2 Stripe of data has a parity version
on drive three which we will call AP.
The B1 and B2 Stripe of data has a parity version
on drive two, we'll call that BP.
And the C1 and C2 Stripe of data has parity on drive one
and we'll call that CP.
You'll notice that the parity blocks are staggered.
It starts with drive three, then drive two, then drive one.
You don't want to have all of the parity on one drive.
So this way we can recreate any data block or portion
of that data block if it fails or if an entire drive fails.
So again, in a RAID five environment,
one hard drive can fail and you'll still be able
to get access to the data.
And we could still recreate the data once we replace
that drive, but if a second drive was to fail,
you'd be in trouble.
That's why there's RAID six.
With RAID six, you have additional parity
and up to two drives can fail while still
being fault tolerant.
So you have to decide how much fault tolerance do we need?
How much money do I have for hard drives?
And that will help you decide whether
you're gonna use RAID five or RAID six.
Here's an example of a RAID five array that
is controlled by software.
It's running in Windows in the disc management Window
and we have our three drives here.
They're labeled as disc one, disc two and disc three.
Collectively, they make up the S volume
and that light blue, that baby blue
in the header means RAID five volume
for this operating system.
If you write data to this volume,
it is striped across the three drives,
but parity information is included as well
for each data block.
If one drive was to fail, you would need
to replace that drive and then rebuild
the array within disc management
and rebuild the data on new drive,
or you could attempt to restore from backup.
Now, software's great, but hardware is always superior.
And you're definitely gonna see hardware based
RAID five arrays.
And here's an example of some hardware
that you might see used in the array.
There is a controller at the top which can handle
as many as five drives and it's an SATA controller.
And on the bottom, we have three hard drives
that will be connected to the controller.
And again, you have to have three drives minimum
and they should be the same make and model.
The controllers firmware could be accessed previous
to the operating system being booted in the same manner
that we pressed Control + I to get into the RAID firmware
on the Intel motherboard.
But again, you wanna make sure the make and model
of the hard drives is the same.
And if you look closely at these two drives,
you'll see a slight difference.
One, is a 1600AVBS, and the other is a 1600AVJS.
They're both 160 gig drives, but they're slightly different.
And I think the one difference with these
is the cache memory on board.
And that could be a big deal.
You could try it, you could see if it'll work,
but it's not really a good idea.
In addition to that, you see the drive on the left
has been written on, that's always a bad sign as well.
So when you're working with hard drives,
work with new drives, don't just grab anything you can find
that's already been used.
You don't know the condition of that drive.
You wanna use new drives and know
that you're gonna have a shelf life of say two
or three years for those drives.
And you want to know that they're all new,
newly formatted and brand new outta the box.
So watch out for any drives that have been written on,
watch out for slight changes in
the name, slight differences.
Make sure you're using the same drive's
manufacturer and model.
And that's about the end of this sub lesson.