Logical Volume Management - What is LVM & how to use it (and WHY you should use it)

Hello. It's Dorian. And today, I'm going to

cover Logical Volume Management

or LVMs. I'm going to cover what it is,

how to use it, the basics, and why you should use it.

So let's get started.

[Music].

Now, I'm sure many of you have run into

the dreaded low disk space notification,

and then you have to, you know, start

going through your downloads, delete all

your large files, delete your games or whatnot.

And then you have to think about

expanding. So, are you going to add

another hard drive and mount your home partition to it or

start moving files over to there? Or are

you going to buy a larger drive, copy all

your partitions over, then extend the partitions?

Lots of choices, lots of decisions to

make there. But one of the things you could do

is install your Linux distribution on an LVM partition.

Now, when you read about LVM, it

kind of sounds like a RAID array where

you have multiple disks and the data is spanned across that.

In a way, yeah. Okay. It can be, but it

doesn't provide any redundancy or anything, but it does extend your

partitions across multiple disks, similar to

RAID. And what you can do is just keep adding disks to

continue to expand that partition on the fly.

So, in the description down below, I've got a link to an LVM

cheat sheet, and it basically goes

through what I'm going to go through today

step by step with the commands. And you

could follow along with that if you want--

watch the video at the same time, whatever.

And I have it in three different formats

so you can print it up and use it as a hard copy. But to get started,

what is LVM? Well, what it does is it'll take a

group of physical disks and create a volume

group. And then, from within that volume group,

you create logical volumes. So you can have your

swap partition, your root partition, and a home partition.

Then, once you start running out of room,

it's just a matter of adding another disk, and then you can expand your volume group.

And then, within the volume group, you can expand your

logical volumes. So, I'm going to go through that right now and show you.

What I have here is a basic install of Ubuntu. I didn't do anything

other than add a couple of favorites and install GParted.

So, you can see here this is the main hard drive. It has an EFI system

partition and the LVM partition.

Now, I set this when I installed it. It was the regular install

just like any other install, except you would click on the

Advanced button, and then there's an option here to

make it an LVM partition. You can also encrypt it with a password.

That's up to you if you want to do that or not. I don't do that because it

complicates things. And if you're trying to fix something

and it can't access it, it just causes another

layer of issues. But you can turn that on

if you want to. That's completely up to you.

And then you just go ahead and proceed

with the install like you normally would.

If you're trying to convert an existing system into LVM,

there is a way to do it, but it involves creating an

LVM and copying your existing files over

to it and then changing some configurations to make it boot properly

and then deleting the old one. It's not ideal. It can get messy and confusing,

and sometimes it just won't work

depending on how your system is set up.

So, I would say just start fresh--a clean install with LVM

from the beginning. So, this is a fresh install.

I mean, there's a lot of free space and there isn't even a lot of stuff

installed here. But let's just say I am starting to run out of room on my LVM

partition. It's full of games, movies, music, and what have you.

So, what I'm going to do is add another

hard drive into my computer, which I have done. So, if I go

down here, I have sdb. So, I have a 223 GB SSD in here, and I added another 120 GB. It shows up as a 111, but

this is what I added into my system.

And it doesn't matter what's on it because you're going to wipe it

and everything anyway. So, I just have

two EXT4 partitions in here.

So, the thing you're going to want to do is wipe everything out

that's on it. You could do it with fdisk,

but if you're already running a Linux

distribution, you might as well just use

GParted or some type of graphical application like this.

So basically, I'm just going to delete both of these, and I'm going to

create a new partition, take up all the space,

and it's going to be an LVM to PV as it shows up in GParted.

It might just say "Linux LVM" in whatever program you're using, but the important thing is

you're creating the LVM file system. So, add that,

apply, get that done, and then we can

finally get started and start extending our space.

So, next thing you're going to do is open up a terminal window. And I know

a lot of people are going, "Oh, no. Not the terminal." But it's not--

it's not that hard. And you can use

that cheat sheet that I have, and it's not a big deal. I'll walk you

through everything here.

So, some of the commands you're going to use here are pvs.

And before I get started, anything that you use here is going to be

sudo. So, you can do sudo su to become root so you don't have to

keep typing it, but you do have to be root to be able to do it.

So, now this is listing our physical

volumes. This is whatever disks that you

have in your system that have an LVM partition.

So, you can see sda2 is the partition that we're actually using for Ubuntu,

and you can see here it's mounted as vgubuntu,

which is here. Another command to show what's

currently going on is you could do vgs,

and it's going to show you the vgubuntu

volume group. And it is using one physical volume with

one disk, and it contains two logical volumes.

So, let's go ahead and look at lvs, logical volumes. So, the logical volumes--

the two that are listed up here--are root and swap. So, I have the root partition,

which is 222 GB, and I have a swap partition,

which for some reason Ubuntu only made

1 GB, and I'm going to expand that.

There's actually a difference in expanding a swap partition than a

regular partition, so I'm going to go through those steps as well.

So now, if you've used fdisk or another utility and it is not showing up here,

then the command you're going to want to use is pvcreate--

so physical volume create. And you're basically just going to

tell it which physical volume you want added.

Now, this isn't going to do anything because it was already successfully created.

So, if I do sudo pvs, you can see it's there. It was there

before. It's not assigned to any volume group, but if it didn't show up

the first time, it should now show up.

Okay. So, at this point, we have two physical volumes, and we want to

extend our volume group across both

disks. So now what you're going to do here is

sudo vgextend vgubuntu because that is the volume group we want to extend,

and then /dev/sdb1 because we want vgubuntu to extend onto

sdb1. So, we'll do that and successfully extend it.

So, we can go ahead and do pvs,

and now we can see that the volume group

is on both physical hard drives.

So now, at this point, we haven't changed anything with the

root and swap partitions. They are the same size. They are both

still on sda2, the original hard drive. What we have to do now is

extend those into the new space that is

available on the hard drive.

Now, as I mentioned before, I only had the 1 GB of swap partition, which to

me is fine. I actually don't use

any, but if you wanted to resize a swap partition,

this is how you're going to do it. The first thing you're going to do is

turn the swap off. So, the command is swapoff

-a, which will turn off all swap partitions, because you could

have more than one. And now we can resize that swap partition.

So, let's have a look at the logical volumes--the lvs--and you can see that swap_1 is 1 GB.

We need to extend that logical volume now that we have additional space

on the drive. So now we're going

to resize the logical volume of the swap partition.

But one thing that you're going to need to know is the path of

where that volume is physically on the drive.

So I'll explain this here by running lvdisplay. So Logical Volume Display shows

you a lot of information about the logical volumes in your volume group.

Now, you can see here the swap partition is

here: /dev/vgubuntu.

So vgubuntu is acting as a hard drive.

Normally, you'd have /dev/sda1 and whatnot.

Well, this is vgubuntu because it's a volume group, and then swap_1

within that volume group. If you found that confusing, don't worry about it.

The biggest thing you need to know is

you need to know this path in order to resize the partition.

So now we're going to do lvresize

and the path of what you want to

extend. And you're going to do -L (dash capital L), and then you're going to use disk

space here, like gigabytes, megabytes. So, I want an additional

7 gigabytes. So I do +7G. You could do

M if you want an extra 7 megabytes for some reason, but

I'm using gigabytes. So I want an extra 7 gigabytes

added to the current size of that swap

partition. So I'm going to do that, and the logical volume of swap_1

is successfully resized.

So you can see it went from 976 MB to 7.95 GB--

close enough to 8 GB. Now, because it's a swap partition, you need to do

mkswap, and you're going to put that same path again.

It's going to format it--no, it's not going to format it because

you also need to be sudo. Alright, so that's done. And now we can do swapon again:

-a. And if we look at our system monitor, my swap is now showing as 8 GB.

So, perfect. Now, that's swap partitions. That is not

EXT4 root partitions. That's just something I wanted to cover because it's

a different way to do it--because you have to unmount,

recreate the swap filesystem, and remount.

Resizing the root partition is actually a little bit easier.

So again, let's just do lvdisplay. And this is the one we want to resize.

So I'm just going to copy that. And now here, we're going to sudo lvresize,

just like before. And just like before, I could do

-L 100G and then the path.

Now, you'll notice before I put the options here

after--it doesn't really matter if you put it before or after; it will

understand. So I just want to show you that

it doesn't matter how you do it. And this should actually be

a +100G, but I'm not going to do

this. What I want to do is take up all the available remaining space on

that drive, because I took 7 GB of the new drive for the swap partition.

So now the rest of the space--I want to take it all up.

So I'm going to change this to lowercase l, and then I'm going to go

+100%FREE. This means I want to take 100% of the remaining free

space on the new drive--the new

volume group which is now extended onto the new drive, which gave us

extra free space. So now I want to resize this

root partition to take up all of it. You can see what is available

here also by doing a

sudo pvs, and you can see here there's 104 GB

free on the volume group because we've taken

7 away for the swap partition. So this command down here

in the other window is going to add 104 GB to our total free space.

So you can see here the size of root: 218 GB, 202 GB free.

So we're going to go ahead and run our resize command.

And you can see root has changed from 222 GB to 326 GB.

There's one thing that I forgot,

because I'm not reading my own notes on my cheat sheet:

you have to resize the filesystem within the logical volume as well.

So there's a -r that has to go in there as well.

So just run that, and it will also

resize the filesystem within the logical volume.

So now if we go ahead and

run this again, we can see here that root

used to be 218 GB with 202 GB free, and it is now 321 GB with

301 GB free. So now we have extended

our partition for root and swap across two physical drives.

So now, going back to GParted here--when this drive

fills up and it's out of space, the data is just going to start

spilling over into sdb1, the new hard

drive that you just added. You can see here the mount point for the LVM

partition is vgubuntu, and if you look on sdb,

the mount point is also vgubuntu.

And then after this, if you fill this disk up,

you do the same thing and you just add

another drive and extend onto that one as well.

However, if that happens on the drive you've added,

I would strongly consider getting a much larger hard drive

if you're going to add one so that it doesn't happen again.

So this is very handy for if you're running a server

and you're just collecting data, if you have a lot of pictures

and you have a computer that you just

use for working on pictures or videos,

and you just keep, you know, collecting large files

over and over and you just run out of space--well, throw in another hard drive.

And run out of space? Throw in another hard

drive. Now, the big downside to this is

shrinking--going the opposite, if

you want to remove one of your physical disks.

It's a little more complicated, and I'm

not going to go through it because I have tried it, and

three out of four times, the system wouldn't boot. Because you can

shrink your volumes and you can move the data off the physical disks.

But there's still a really good chance that you're going to lose data,

and something's going to go wrong. And three out of four times,

something went wrong, and the system wouldn't boot. So I just kept

trying and trying and trying. Actually, I did try another time.

So three out of five times, it failed. Two succeeded, but it took some

messing around with, and I don't know.

It's not--it's not something you want to do. This is better for just

expanding and expanding. So all this

in a nutshell--well, a long nutshell--but I tried to keep it short and simple.

All this is how you would continue expanding your drives with LVM.

Key points are: start with an LVM to begin with right

off the bat, get a larger hard drive than

you think you would need if you're adding one,

and remember that shrinking is not a

good option and terrible things can happen.

And yeah, I hope this helps you out. So don't forget to subscribe.

Don't forget to like the video. Share it on your social media. And until next time, bash on.

[Music].