Add storage to your Fedora system with LVM

Sometimes there is a need to add another disk to your system. This is where Logical Volume Management (LVM) comes in handy. The cool thing about LVM is that it’s fairly flexible. There are several ways to add a disk. This article describes one way to do it.

Heads up!

This article does not cover the process of physically installing a new disk drive into your system. Consult your system and disk documentation on how to do that properly.

Important: Always make sure you have backups of important data. The steps described in this article will destroy data if it already exists on the new disk.

Good to know

This article doesn’t cover every LVM feature deeply; the focus is on adding a disk. But basically, LVM has volume groups, made up of one or more partitions and/or disks. You add the partitions or disks as physical volumes. A volume group can be broken down into many logical volumes. Logical volumes can be used as any other storage for filesystems, ramdisks, etc. More information can be found here.

Think of the physical volumes as forming a pool of storage (a volume group) from which you then carve out logical volumes for your system to use directly.

Preparation

Make sure you can see the disk you want to add. Use lsblk prior to adding the disk to see what storage is already available or in use.

$ lsblk
NAME                   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
zram0                  251:0    0  989M  0 disk [SWAP]
vda                    252:0    0   20G  0 disk
├─vda1                 252:1    0    1G  0 part /boot
└─vda2                 252:2    0   19G  0 part
└─fedora_fedora-root   253:0    0   19G  0 lvm  /

This article uses a virtual machine with virtual storage. Therefore the device names start with vda for the first disk, vdb for the second, and so on. The name of your device may be different. Many systems will see physical disks as sda for the first disk, sdb for the second, and so on.

Once the new disk has been connected and your system is back up and running, use lsblk again to see the new block device.

$ lsblk
NAME                   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
zram0                  251:0    0  989M  0 disk [SWAP]
vda                    252:0    0   20G  0 disk
├─vda1                 252:1    0    1G  0 part /boot
└─vda2                 252:2    0   19G  0 part
└─fedora_fedora-root 253:0    0   19G  0 lvm  /
vdb                    252:16   0   10G  0 disk

There is now a new device named vdb. The location for the device is /dev/vdb.

$ ls -l /dev/vdb
brw-rw----. 1 root disk 252, 16 Nov 24 12:56 /dev/vdb

We can see the disk, but we cannot use it with LVM yet. If you run blkid you should not see it listed. For this and following commands, you’ll need to ensure your system is configured so you can use sudo:

$ sudo blkid
/dev/vda1: UUID="4847cb4d-6666-47e3-9e3b-12d83b2d2448" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="830679b8-01"
/dev/vda2: UUID="k5eWpP-6MXw-foh5-Vbgg-JMZ1-VEf9-ARaGNd" TYPE="LVM2_member" PARTUUID="830679b8-02"
/dev/mapper/fedora_fedora-root: UUID="f8ab802f-8c5f-4766-af33-90e78573f3cc" BLOCK_SIZE="4096" TYPE="ext4"
/dev/zram0: UUID="fc6d7a48-2bd5-4066-9bcf-f062b61f6a60" TYPE="swap"

Add the disk to LVM

Initialize the disk using pvcreate. You need to pass the full path to the device. In this example it is /dev/vdb; on your system it may be /dev/sdb or another device name.

$ sudo pvcreate /dev/vdb
Physical volume "/dev/vdb" successfully created.

You should see the disk has been initialized as an LVM2_member when you run blkid:

$ sudo blkid
/dev/vda1: UUID="4847cb4d-6666-47e3-9e3b-12d83b2d2448" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="830679b8-01"
/dev/vda2: UUID="k5eWpP-6MXw-foh5-Vbgg-JMZ1-VEf9-ARaGNd" TYPE="LVM2_member" PARTUUID="830679b8-02"
/dev/mapper/fedora_fedora-root: UUID="f8ab802f-8c5f-4766-af33-90e78573f3cc" BLOCK_SIZE="4096" TYPE="ext4"
/dev/zram0: UUID="fc6d7a48-2bd5-4066-9bcf-f062b61f6a60" TYPE="swap"
/dev/vdb: UUID="4uUUuI-lMQY-WyS5-lo0W-lqjW-Qvqw-RqeroE" TYPE="LVM2_member"

You can list all physical volumes currently available using pvs:

$ sudo pvs
PV         VG            Fmt  Attr PSize   PFree
/dev/vda2  fedora_fedora lvm2 a--  <19.00g     0
/dev/vdb                 lvm2 ---   10.00g 10.00g

/dev/vdb is listed as a PV (phsyical volume), but it isn’t assigned to a VG (Volume Group) yet.

Add the pysical volume to a volume group

You can find a list of available volume groups using vgs:

$ sudo vgs
VG            #PV #LV #SN Attr   VSize   VFree
fedora_fedora   1   1   0 wz--n- 19.00g    0

In this example, there is only one volume group available. Next, add the physical volume to fedora_fedora:

$ sudo vgextend fedora_fedora /dev/vdb
Volume group "fedora_fedora" successfully extended

You should now see the physical volume is added to the volume group:

$ sudo pvs 
PV        VG            Fmt  Attr PSize   PFree
/dev/vda2 fedora_fedora lvm2 a–   <19.00g 0
/dev/vdb  fedora_fedora lvm2 a–   <10.00g <10.00g

Look at the volume groups:

$ sudo vgs
VG            #PV #LV #SN Attr  VSize  VFree
fedora_fedora 2   1   0   wz–n- 28.99g <10.00g

You can get a detailed list of the specific volume group and physical volumes as well:

$ sudo vgdisplay fedora_fedora
--- Volume group ---
VG Name               fedora_fedora
System ID
Format                lvm2
Metadata Areas        2
Metadata Sequence No  3
VG Access             read/write
VG Status             resizable
MAX LV                0
Cur LV                1
Open LV               1
Max PV                0
Cur PV                2
Act PV                2
VG Size               28.99 GiB
PE Size               4.00 MiB
Total PE              7422
Alloc PE / Size       4863 / 19.00 GiB
Free  PE / Size       2559 / 10.00 GiB
VG UUID               C5dL2s-dirA-SQ15-TfQU-T3yt-l83E-oI6pkp

Look at the PV:

$ sudo pvdisplay /dev/vdb
 --- Physical volume ---
 PV Name               /dev/vdb
 VG Name               fedora_fedora
 PV Size               10.00 GiB / not usable 4.00 MiB
 Allocatable           yes
 PE Size               4.00 MiB
 Total PE              2559
 Free PE               2559
 Allocated PE          0
 PV UUID               4uUUuI-lMQY-WyS5-lo0W-lqjW-Qvqw-RqeroE 

Now that we have added the disk, we can allocate space to logical volumes (LVs):

$ sudo lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
root fedora_fedora -wi-ao---- 19.00g

Look at the logical volumes. Here’s a detailed look at the root LV:

$ sudo lvdisplay fedora_fedora/root
--- Logical volume ---
LV Path                /dev/fedora_fedora/root
LV Name                root
VG Name                fedora_fedora
LV UUID                yqc9cw-AvOw-G1Ni-bCT3-3HAa-qnw3-qUSHGM
LV Write Access        read/write
LV Creation host, time fedora, 2020-11-24 11:44:36 -0500
LV Status              available
LV Size                19.00 GiB
Current LE             4863
Segments               1
Allocation             inherit
Read ahead sectors     auto
- currently set to     256
Block device           253:0

Look at the size of the root filesystem and compare it to the logical volume size.

$ df -h /
Filesystem                      Size  Used Avail Use% Mounted on
/dev/mapper/fedora_fedora-root   19G  1.4G   17G   8% /

The logical volume and the filesystem both agree the size is 19G. Let’s add 5G to the root logical volume:

$ sudo lvresize -L +5G fedora_fedora/root
Size of logical volume fedora_fedora/root changed from 19.00 GiB (4863 extents) to 24.00 GiB (6143 extents).
Logical volume fedora_fedora/root successfully resized.

We now have 24G available to the logical volume. Look at the / filesystem.

$ df -h /
Filesystem                      Size  Used Avail Use% Mounted on
/dev/mapper/fedora_fedora-root   19G  1.4G   17G   8% /

We are still showing only 19G free. This is because the logical volume is not the same as the filesytem. To use the new space added to the logical volume, resize the filesystem.

$ sudo resize2fs /dev/fedora_fedora/root
resize2fs 1.45.6 (20-Mar-2020)
Filesystem at /dev/fedora_fedora/root is mounted on /; on-line resizing required
old_desc_blocks = 3, new_desc_blocks = 3
The filesystem on /dev/fedora_fedora/root is now 6290432 (4k) blocks long.

Look at the size of the filesystem.

$ df -h /
Filesystem                      Size  Used Avail Use% Mounted on
/dev/mapper/fedora_fedora-root   24G  1.4G   21G   7% /

As you can see, the root file system (/) has taken all of the space available on the logical volume and no reboot was needed.

You have now initialized a disk as a physical volume, and extended the volume group with the new physical volume. After that you increased the size of the logical volume, and resized the filesystem to use the new space from the logical volume.

FAQs and Guides Using Hardware

12 Comments

  1. RG

    Good to know we’ve BTRFS as default since Fedora 33, e.g. with all features and more as a replacement of LVM.

    • hammerhead corvette

      LLVM is a good alternative to BTRFS for those who might questions BTRFS’s reliability and downsides in certain scenarios. BTRFS is definitely not a one size fits all solution. LLVM + XFS is a very robust and trusted alternative.

      • jama

        XFS does not allow partition shrinking, which is one of many great benefits of LVM. I do, and have been using LVM + EXT4 for several years, and sometimes there’s also a need to shrink a filesystem, which LVM handles on-the-fly with –resizefs -parameter; ‘lvresize –size -100G –resizefs ‘, so there’s no need to run ‘resize2fs’ separately.

      • Jonathan

        LLVM is a compiler.

      • Sergey

        +1
        The most important thing has been tested for years and has the main principle of unix – one utility does one thing but does it well !

      • Vektor

        It’s LVM, for Logical Volume Management.
        LLVM is something completely different:
        https://en.wikipedia.org/wiki/LLVM

  2. didli

    Excellent article anyway. A very clean and simple way to present how things work for LVM, thank you.

  3. Antonio Dias

    It is not mandatory but always a good practice to create a partition with type Linux LVM and then make it your PV.

    • Tim Bosse

      I went back and forth on initializing the pv on the partiton or directly on the disk. There is really only one use case [1] where it is better practice to initialize on the partition. It is a valid use case, though the argument is fairly old [2].

      Initializing on a partition is beneficial when multibooting an operating system that doesn’t understand LVM. At the very least, the other operating systems would see the disk is partitioned. Hopefully it would let you know not to use that partition on another OS.

      That’s one of the reasons the article mentions the method described is just one way to add a disk, not the only way. From my experience, I only have Fedora running on my systems and they always use LVM for all disks, so that’s how I described it.

      [1] https://tldp.org/HOWTO/LVM-HOWTO/initdisks.html
      [2] https://www.sourceware.org/lvm2/ (under documentation, the source is under a very-dated howto as described by the maintainers)

      • Antonio Dias

        Yeap. I agree it really does not matter when you are using it on your personal Fedora workstation, with just one disk. But I guess LVM will not be the best solution in that case (and I believe the team that develops Fedora agrees, judging by their move replacing LVM/XFS with BTRFS).

        But the keyword in [1] is “management”. When you managing a server with hundreds of LUNs, “marking” used disks with partitions is a quick way to tell a new disk apart from the already used ones.

        Anyway, as you pointed, is just a matter of management ability choice.

  4. Joao Rodrigues

    The downside is that LVM does not know anything about the filesystem that is on a logical volume, so if you want to move a 1 TB logical volume from one physical disk to another, it will read and write 1 TB of data, even if the filesystem underneath is empty.

    I also vaguely remember that LVM snapshots were kind of weird, as they grow in size the more you change the original volume, and could run out of space.

  5. JayBee

    Hi,
    Since I didn’t find a clear representation schema on the internet, I made my own representation schema that gather all layers related to storage (FS, LVM, mdadm, partitions, disks). Is my representation correct?
    Feel free to use it, and do not hesitate to improve the design to make it sexier.
    https://www.reddit.com/r/linux4noobs/comments/gtwnlh/is_my_diagram_correct_only_soft_raid_is/

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