LVM Configuration Guide - Linux

We all might be familiar with the term LVM i.e. Logical Volume Mapping. In Linux, this is a device mapper framework that provides the ability to logically manage the volumes for the Linux Kernel. The main intent of doing so, to dynamically resized the volumes as per the requirements on go. This is basically a layer of abstraction between the physical drives and you. One can expand and shrink the volumes on fly.

Let's see below step by step how one can achieve that

Scenario : 1 Root device, 2 External devices are attached to the ubuntu machine. Using all 3, will apply the LVM logic and see how it can be configured. Below Physical Hard drive could be anything like USB etc.

1. Root Device
2. External Device 1 i.e. Physical Hard drive
3. External Device 2 i.e. Physical Hard drive

Now, if I give you a pictorial view how the logic works, this configures in 3 steps

• Looking physical Hard drives
• Create Physical Volume
• Create Volume Group
• Create Logical Volume

Login to your machine and open the terminal. Initially, you should know how many devices my machine has. This can be achieved with the command

1. Looking for Physical Hard Drives

df -h

The output would be as:

/dev/root       7.7G  2.8G  4.9G  37% /
devtmpfs        486M     0  486M   0% /dev
tmpfs           490M     0  490M   0% /dev/shm
tmpfs            98M  812K   98M   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           490M     0  490M   0% /sys/fs/cgroup
/dev/loop1       97M   97M     0 100% /snap/core/9804
/dev/loop0       29M   29M     0 100% /snap/amazon-ssm-agent/2012
/dev/loop2       98M   98M     0 100% /snap/core/9993
/dev/loop3       56M   56M     0 100% /snap/core18/1885
/dev/loop4       71M   71M     0 100% /snap/lxd/16922
tmpfs            98M     0   98M   0% /run/user/1000

This shows, we've /dev/root device having ~8GB of size. Currently it is not showing the 2 External Physical drives which we've attached

2. Now we need to create the Physical Volume with the commands, but before that we need to check and need to know the names of the External Drives. This can be achieved with the diskscan command - which basically tells what other external drives you've with the machine

lvmdiskscan

/dev/loop0 [     <28.09 MiB]
  /dev/loop1 [      96.62 MiB]
  /dev/xvda1 [      <8.00 GiB]
  /dev/loop2 [      97.06 MiB]
  /dev/loop3 [      55.32 MiB]
  /dev/loop4 [      70.56 MiB]
  /dev/xvdf  [       5.00 GiB]
  /dev/xvdg  [       3.00 GiB]
  2 disks
  6 partitions
  0 LVM physical volume whole disks
  0 LVM physical volumes

Now, you can see you've /dev/xvdf and /dev/xvdg External Drives and it is clearly showing 0 LVM physical volume whole disks

3. Now, as per the step we will create Physical Volume as per below

sudo pvcreate /dev/xvdf
//successfully created
sudo pvcreate /dev/xvdg
//successfully created

To verify the Physical Volumes, check with command

sudo pvs

 /dev/xvdf     lvm2 ---  5.00g 5.00g
 /dev/xvdg     lvm2 ---  3.00g 3.00g

The above shows that Physical Volume create

Now, we need to create Volume Group and to take both these external drives into that

sudo vgcreate mygroup /dev/xvdf /dev/xvdg

Volume group "mygroup" successfully created

//Successfully created

***Verify with the command***

sudo vgs

 
VG      #PV #LV #SN Attr   VSize VFree
mygroup   2   0   0 wz--n- 7.99g 7.99g

Now, create the Logical Volumes

Please note: I've 2 External HDD of 5GB and 3GB. I am creating Logical volume of 4GB first, then 3GB and leftover will be as separate. So, ideally it will be 3 Logical volumes

//Creation of First Logical Volume

sudo lvcreate -L 4GB -n logical1 mygroup

//Creation of Second Logical volume

sudo lvcreate -L 3GB -n logical2 mygroup

//For Left-over space

sudo lvcreate -l 100%FREE -n logical-final mygroup

***Results can be seen***

 VG      #PV #LV #SN Attr   VSize VFree LSize    LV
  mygroup   2   3   0 wz--n- 7.99g    0     4.00g logical1
  mygroup   2   3   0 wz--n- 7.99g    0     3.00g logical2
  mygroup   2   3   0 wz--n- 7.99g    0  1016.00m logical-final