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Hey guys and welcome back. So what I want to talk to you about in this skill right here

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is the concept of LVM. Now what LVM actually stands for, it stands for the logical volume

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manager or sometimes referred to as logical volume management. So let me first begin

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describing what logical volume manager actually does for us by giving you a scenario. So let's

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say that you want to have additional storage space, okay? Simply put, what you actually have

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right now is not cutting it. So you actually ask if you can get an expansion of your current

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storage situation. So let's say for whatever reason you maybe happen to need, let's just say

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another 15 gig of storage. And in order to be helpful to you, well your team does supply you

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with this extra 15 gig. But what they do is they come and they bring three different drives. One is

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a 5 gig drive, the other is a 5 gig drive, and the last one is a 5 gig drive. Now in total,

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this does give you 15 gigabits of additional storage. But what if maybe the software or the

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application you need actually needs the entire 15 gig. What disk exactly then are you going to put

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this on? Because you can't put the 15 gig on this 5 gig, it's not enough, nor this one, nor this one.

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Instead, what you would have to do is you would have to aggregate these devices and combine them so

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that they could actually yield their combined storage space of 15 gigabytes. Now this is exactly

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what we're talking about when we mention the types of problems that LVM can actually solve. So let me

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first describe to you the basic architecture of how LVM works. And then we'll list some of the

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advantages of using LVM and we'll also mention some of the potential downfalls of using LVM.

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Honestly, I will say that I do believe LVM is an absolutely amazing technology. This is something

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you absolutely want to learn, not just for the purposes of the LPIC2 examination, but as a Linux

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engineer. This is something that's going to be so useful to you on a very regular basis, in my opinion.

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So let's dig into the architecture. Let's find out how this technology works. Let's see how it's

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going to solve this problem. So well, why don't we just dig right into it right away then shall we?

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So what I'll do is I will clear my screen. Okay, so let me first begin by highlighting

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three main concepts that are going to make up the LVM architecture. One is known as APV. The next one

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is known as AVG and the last one is known as an LV. Now what are these rather cryptic sounding

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names? Well, it actually isn't quite so cryptic. The first one is simply called a physical volume.

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The next one is called a volume group and the last one is called a logical volume. So let's

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actually tackle these one by one and then see how they all actually relate to one another. So we'll

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start off with the very first one, the PV, the physical volume. Now, when you have a whole bunch

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of different physical devices, like in the example I said, you are presented with three different

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five gigabit hard drives, five here, five here and five here. These are actually physical hard

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drives we're talking about here. Okay, someone actually walks in to the room with three hard drives

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in their hands and gives them to you. Now, in order to be able to use these devices as PVs, physical

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volumes, we would take them and we would have to mark it with an LVM header. We'll get to see how we

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actually do this in the next nugget, but really just conceptualize the PVs as the actual disks that

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we're using, the block devices that we can ultimately assign a header to be used as a physical volume.

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So now if we can use these as a physical volume, these three different devices, and the problem is

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as we denoted that we need 15 gigabytes of storage combined, not three individual five

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gigabytes of storage. You can probably guess what we want to do. We want to combine these

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and when we actually combine these three physical volumes into one big chunk, so we aggregate it

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as 15 gig, that aggregation is known as the volume group. This is the VG that we create.

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Like I say, this would now be combined to be 15 gigabytes. So really all we're talking about with

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respect to the volume group, this is the big logical chunk that is made up of multiple physical

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volumes. Pretty cool. Now, now that we actually have this big 15 gigabit logical chunk, if we

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actually want to segment this, we could segment it into our logical volume. So let's say we split it

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in half and we give 7.5 gig here and 7.5 gig here. This would be one logical volume and this would be

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another logical volume. Now, right now, it may not be apparent why this is useful, you're thinking,

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okay, so we had these multiple disks, we combined them just so we could then chop them up further.

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But the reality is, this is very, very flexible. So let me show you. For a start, one thing is that

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the physical devices do not have to be the same size. In my example, I gave a very simple example

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of three 5 gigabyte devices. That doesn't actually have to be the case. Let's say we had, I don't know,

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one device here, which was 2 gig, and the second device was 5 gig, and maybe another device was

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3 gig, and we had one here for 20 gig, a little bit bigger. So what we have now are four distinct

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devices, each with their own space. Now, let's say we wanted to have three distinct projects,

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whatever that may actually comprise of, and each of those projects were going to take up 10 gig each.

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What disk could you choose right now in order to fill this out? Well, you could put two of the

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projects on this one here, because you could have 10 and 10, and now this one would be completely

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full. But what about that last project that requires 10 gig? Which device would you choose?

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The reality is you can't, but what we could do is we could combine all of these. So we had 20,

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add 3, which is 23, add 5, which is 28, add 2, which is 30. So we say let's take these four

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individual devices, let's create a volume group of 30, and we could put the three projects on

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this particular volume group. But what if, let's say for example, you wanted to have each one on a

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separate partition, let's just say, or using a different file system? Well, like I say, we could

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carve this up. So now we have this 30 gigabyte chunk, so that this is 10, and this is also 10,

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and we could have partition one, partition two, partition three, all with different file systems

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if we so choose, and we could put the first project here, the second project here, and the third

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project here. And under the hood, we are actually utilizing four physical devices, but we are able

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to combine them and segment them however we want. So really, you can gather up these physical devices,

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smash them all together so that they're like one big massive chunk, and you can choose to divide

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and chop this up like a pizza in whatever sizes you actually wish. So when you're using LVM,

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as we can see here, we can aggregate cheap physical disks to make one large logical chunk and chop

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that up as we wish. When we're dealing with LVM, we don't just get our physical disks and then,

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you know, blend it into a large volume group, subdivide it as we may wish, and then we're done.

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If we want to extend our logical volume by adding more disks later on, then we have the

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ability to extend this because like I say, around LVM, we have tons and tons and tons of

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flexibility. Similarly, if we want to shrink our LVM, we can reduce the size, we can reduce the

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disks that we are using, or we can just shrink the logical size of particular partitions,

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whatever it may be. All of this is available to you when you choose to use LVM. This is why it's

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so, so useful. So the question is, how exactly do we utilize this technology? How can we actually

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build these volume groups and subdivide them into logical volumes? Well, we will absolutely be

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looking at that in the very next nuggets. I hope this has been informative for you and I'd like to

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thank you for viewing.