- [Instructor] In this segment,
we're going to take another look at rate configurations,
specifically disk mirroring and disk striping.
The raid combines multiple disk drive components
into one or more logical units
for the purposes of fault tolerance, data redundancy,
and/or performance improvement.
The raid can be configured for mirroring, striping, or both.
Disk mirroring is a process of writing data
on two partitions on separate disks,
that's referred to as Raid 1.
And you can see from our illustration,
we have two identical disks.
We have Disk 0 and we have Disk 1.
And everything that's being written to Disk 0
is also being written to Disk 1.
So we have complete redundancy.
We can lose either drive
and continue to be functional and operational.
Matter of fact, our user will probably not even notice
that a drive is gone.
So that's referred to as raid level 1 disk mirroring.
But we still have a single point of failure
with traditional disk mirroring
because we only have one drive controller.
One drive controller, two drives,
our single point of failure is going to be that controller.
So best practices would dictate that we add a controller
to mitigate the risk associated
with a single point of failure or an SPOF.
So in the configuration where each drive
has its own controller, we refer to that as disk duplexing.
So we went with disk mirroring, two drives, one controller,
to disk duplexing, two drives,
each having their own controller.
Now let's take a look at disk striping in Raid 5.
Disk striping is a process dividing data into blocks
and spreading the data blocks
across multiple storage devices.
Disk striping is a performance enhancement.
So where do we get the redundancy?
We add in parity bits.
So what we're doing is we're writing a parity bit
with each stripe,
and that parity bit can be used to recreate the data
if any one drive is lost or fails.
So let's look at our Raid 5 configuration.
We've got four drives here.
Looking at four drives.
And watch our striping across.
Stripe A1, A2, A3.
Oh, there's our parity bit.
Our next stripe, B1, B2, parity bit, then B3.
C1, parity bit, C2, C3.
And then parity bit, D1, D2, D3.
We can lose any one of these drives,
and the data on that failed or lost drive
will be recreated from each of the remaining parity bits.
So disk striping with parity
gives us both the performance enhancement
and fault tolerance.
Now, what do we do if we lose a component?
Well, we're going to have to replace
that component or that drive.
And just as a refresher,
we have different ways that we do replacements
referred to as swaps.
A cold swap is when we need to power down a system
in order to replace a component.
A warm swap is the ability to insert and remove hardware
while the system is in a suspended state.
And the hot swap is the ability to insert
and remove hardware while the system is running.
Now, drive redundancy is absolutely
a key component of resiliency.
It's an investment that recognizes the importance
of system availability.
And that, my friends, is a closer look at Raid 1 and Raid 5.