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Let's go over the RAID. What exactly RAID
is? A RAID stands for redundant array of
independent disks, or sometimes often
referred to as inexpensive disk. And
RAID, why do we need RAID? Well to
create a redundancy, meaning if one disk
dies, you have another disk, right? You
don't want to lose your data if one of
one of your primary disks dies. So
that's the primary reason we have RAID.
And there are different types of RAIDs.
The main ones that we will cover in this
lesson are three RAIDs, RAID 0, 1, and
5. And how do they work? Let's go
over them. In RAID0, you have one
disk, that is, let's say five gig. You
add another disk, that becomes 10 gig.
So you put them together, and then five
plus five becomes 10 gig, right?
Perfect. So you are writing to both disc
one here, one there, it's going
across, it's faster, of course. But what
happens if you lose one disk? Well, you
are out of luck. Why? Because you have lost all
your data. So there is the most of the
time RAID0 is used for like data
warehousing or backups that you really
rarely going to use. So things like
that. So you do need to add a couple of
disk, physical disks, together to make one
big disk. That's how RAID0 is
mostly used. Let's talk about RAID1,
that will eliminate that disadvantage of
RAID0 where we lose one disk, and
then you are out of luck. In RAID1,
you have one disk, and then you have
another disk, but you mirror them
together. Meaning if you have five gig
of space on one, you have to have
five gig on another one. But that does
not mean you have, you're going to have
10 gig together, because you are not
adding them together, you are mirroring
mirroring them together. So if you lose
one disk, that's fine, you still get the
get your data from the other disk. But
there is another disadvantages to RAID1,
and that is slow. It is slow,
because it has to replicate everything
from one disk to another so that some
some time gets a slow read and slow
writes. Then to solve all these problems
0 and 1, what do we do
then? 0, 1 has, we have a risk to lose data,
RAID1, we have slow read and
write. So we come up with RAID5, and
RAID5, you have one disk right? Then
you have another disk, but this time you
don't just add to it, you actually copy
everything to the second one as well.
But in RAID5, you have to have three
or more disks. Why? Because the way, the
way RAID5 works is, it will write to
the first disk, and it will put some
information about that data to the
second disk. It will write to the second
disk and it will put some of that
information that it has written to
the third disk, and it goes around like
a round robin like that. So in case you
lose one disk, which doesn't matter if
it's a first, second or third, you will
have the information of the lost data
on one of the disks that you still have.
That's how you create RAID5. But in
this case, you're not going to have like
5, 5, 5, 15, because you have to write some of
the disk information that's parity to
some other disk as well. So this way you
can retrieve that information. So in
order to put that information somewhere,
it needs to reserve that space for it.
And that's where we get out of it like
12 or 13 gig of space. So that's how
RAID works. And the reason I am covering
RAID in this training is because that's
one of the very basic questions often
been asked during interviews. And as a
system administrator when you do become
a system administrator in Linux
environment, you will have to create
RAID at a hardware level. When you have
a server coming into your corporate
environment, you will have to configure
a RAID. And the difference between, the
primary difference between RAID and LVM
is that RAID is mostly configured on
the physical system, physical servers,
and sorry, not physical, physical disks.
Whereas LVM is mostly configured on a
virtual or logical disks. So that's the
primary difference. So please remember
it if you want to learn more about other
RAIDs, I would encourage you to go
online and find out about other RAIDs.
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