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

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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 first 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 a lvm

cheat sheet and it basically goes

through what i'm going to go through

today

step by step with the commands and you

can 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 g parted

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 a

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 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'm

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 gig

ssd in here and i added another 120 gig

shows up as 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 anyways so i just have

two ext4 partitions in here

so the first 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

g parted 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 g parted it might

just say linux lvm and whatever

um 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 the 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 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 vg

ubuntu

which is here another command to show

what's

currently going on is you could do vg's

and it's going to show you the vg ubuntu

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 gigs and i have a swap

partition

which for some reason ubuntu only made

one gig 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 pv create 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 vg extend vg ubuntu

because that is the volume group we want

to extend

and then dev sdb1

because we want vg ubuntu 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 second hard drive

now as i mentioned before i only had

the one gig of swap partition which to

me

is 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 first

thing you're going to do is

turn the swap off so the command is swap

off

dash a which will turn off the swap

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 one

is one gig we need to extend that

logical volume now that we have

additional space

on the second 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 lv

display 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 so slash dev slash vg ubuntu

so vg ubuntu is acting as a hard drive

normally you'd have dev slash dev sda1

and whatnot

well this is fiji ubuntu because it's a

volume group and then swap one

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 lv resize

and the path of what you want to

extend and you're going to do dash

capital

l and then you're going to use disk

space here like gigabytes megabytes so i

want an additional

seven gigabytes so i do plus seven g you

could do

m if you want an extra seven megabytes

for some reason but

i'm using gigabytes so i want an extra

seven gigabytes

added to the current size of that swap

partition so i'm going to do that

and the logical volume of swap one

successfully resized

so you can see it went from 976 megs to

7.95 gigs

close enough to eight gigs now because

it's a swap partition you need to do

make swap 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 all right

so that's done and now we can do swap on

again

dash a and if we look at our system

monitor

our swap is now showing as eight gigs so

perfect

now that's small 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 file system and

remount

resizing the root partition is actually

a little bit easier

so again let's just do lv display

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 lv

resize

just like before and just like before i

could do

dash l and 100 gigs

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 plus 100 gigs 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

seven gigs 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

plus 100 percent

free this means

i want to take 100 of the remaining free

space

on the new drive the 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

zuru pvs

and you can see here there's 104 gigs

free on the volume group because we've

taken

seven away for the swap partition so

this command down here

in the other window is going to add 104

gigs to our total free space

so you can see here the size of

root 218 gigs 202 gigs free

so we're going to go ahead and run our

resize command

and you can see root has changed from

222 gigs

to 326 gigs there's one thing that i

forgot

because i'm not reading my own notes on

my cheat sheet

is you have to resize the file system

within the logical volume as well

so there's a dash r that has to go in

there as well

so just run that and it will also

resize the file system within the

logical volume

so now if we go ahead and

run this again

we can see here that root

used to be 218 gigs with 202 free

and it is now 321 gigs with

301 gigs free so now we have extended

our partition for root and swap across

two physical drives

so now going back to g parted 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 vg ubuntu and if you look on sdb

the mount point is also vg ubuntu 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 second

drive you've added

i would strongly consider getting a much

larger hard drive

if you're going to add a third 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 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 gonna lose data

and something's gonna 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 it

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

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on your social media and until next time

bash on

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