LVM

2020-10-31 (2022-11-01)
LVM filesystem linux sysadmin

LVM stands for Logical Volume Manager, a mechanism that provides an alternative method of managing storage systems than the traditional partition-based one. In LVM, instead of creating partitions, you create logical volumes, and then you can just as easily mount those volumes in your filesystem as you'd a disk partition.

One exception to the previous statement is that you can not use logical volumes for /boot. That is because GRUB (the most common bootloader for Linux) can't read from logical volumes. The well-known alternative to GRUB, systemd-boot on the other hand reads only vfat filesystems, so that's not going to work either.

Components of LVM

There are three main components to LVM:

Physical Volumes
Volume Groups
Logical Volumes

The main advantage of LVM is how easy it is to resize a logical volume or volume group. It abstracts away all the ugly parts (partitions, raw disks) and leaves us with a central storage pool to work with.

If you've ever experienced the horror of partition resizing, you'd wanna use LVM.

Configure LVM

LVM Installation

Install Ubuntu with encrypted LVM using your main hard drive (assumed /dev/sda).

Layer 1: Hard Drives, Partitions, Physical Volumes

Hard Drives

Start with disk scan to review available disks:

sudo lvmdiskscan

Partitions

If your secondary hard drive (/dev/sdb) is blank, create a full sized partition on it (/dev/sdb1).

Do another lvmdiskscan and you'll see the /dev/sdb1 partition listed as well (if it wasn't already there before).

Physical Volumes

Using pvscan you'll see all your physical volumes:

sudo pvscan

Create a new physical volume for your /dev/sdb1 partition:

sudo pvcreate /dev/sdb1

root@gerbil:/home/dwebb# pvcreate /dev/sdb1
WARNING: ext4 signature detected on /dev/sdb1 at offset 1080. Wipe it? [y/n]: y
  Wiping ext4 signature on /dev/sdb1.
  Physical volume "/dev/sdb1" successfully created.

WARNING: If you wish to preserve the content of /dev/sdb1, type n when prompted to wipe the disk.

Layer 2: Volume Groups

Now we need to add the new Physical Volume to the Volume Group.

List your Volume Groups using vgscan:

vgscan

Found volume group "vgubuntu" using metadata type lvm2

Add the new Physical Volume to the Volume Group using vgextend:

vgextend vgubuntu /dev/sdb1

Volume group "vgubuntu" successfully extended

Now let's check out the current status of the Volume Group:

vgdisplay vgubuntu

--- Volume group ---
VG Name               vgubuntu
System ID             
Format                lvm2
Metadata Areas        2
Metadata Sequence No  4
VG Access             read/write
VG Status             resizable
MAX LV                0
Cur LV                2
Open LV               2
Max PV                0
Cur PV                2
Act PV                2
VG Size               267.05 GiB
PE Size               4.00 MiB
Total PE              68366
Alloc PE / Size       30207 / <118.00 GiB
Free  PE / Size       38159 / <149.06 GiB
VG UUID               1vlT1S-hr1t-NWXg-5EWR-m5dp-mSnu-wuvWvW

Layer 3: Logical Volumes, File Systems

Logical Volumes

Scan the current Logical Volumes with lvscan:

lvscan

ACTIVE            '/dev/vgubuntu/root' [117.04 GiB] inherit
ACTIVE            '/dev/vgubuntu/swap_1' [976.00 MiB] inherit

Create a New Logical Volume

Create a new Logical Volume using lvcreate:

lvcreate -L 149G vgubuntu

Logical volume "lvol0" created.

Scan the current Logical Volumes with lvscan:

lvscan

ACTIVE            '/dev/vgubuntu/root' [117.04 GiB] inherit
ACTIVE            '/dev/vgubuntu/swap_1' [976.00 MiB] inherit
ACTIVE            '/dev/vgubuntu/lvol0' [149.00 GiB] inherit

Extend an Existing Logical Volume

Alternatively, extend an existing logical volume with the newly created unallocated space using lvextend:

lvextend -l +100%FREE /dev/vgubuntu/root

Using df -h you will see that the filesystem size hasn't changed yet.

To update the filesystem (with ext4 you can do this on the fly), use the resize2fs:

resize2fs /dev/vgubuntu/root

LVM Commands

PV – Physical Volume VG – Volume Group LV – Logical Volume

Layer 1: Hard Drives, Partitions, Physical Volumes

lvmdiskscan – System readout of volumes and partitions pvdisplay – Display detailed info on physical volumes pvscan – Display disks with physical volumes pvcreate /dev/sda1 – Create a physical volume from sda1 pvchange -x n /dev/sda1 – Disallow using a disk partition pvresize /dev/sda1 – Resize sda1 PV to use all of the partition pvresize --setphysicalvolumesize 140G /dev/sda1 – Resize sda1 to 140GB pvmove /dev/sda1 – Move data out of sda1 to other PVs in VG (Note: Free disk space equivalent to data moved is needed elsewhere) pvremove /dev/sda1 – Delete Physical Volume

LVM Layer 2 – Volume Groups

vgcreate vg1 /dev/sda1 /dev/sdb1 – Create a volume group from two drives vgextend vg1 /dev/sdb1 – Add PV to the volume group vgdisplay vg1 – Display details on a volume group vgscan – List volume groups vgreduce vg1 /dev/sda1 – Removes the drive from vg1 (Note: use pvmove /dev/sda1 before removing the drive from vg1) vgchange – Activate/deactivate Volume Groups and change perameteres vgremove vg1 – Remove volume group vg1 vgsplit and vgmerge - Split and merge volume groups vgrename – Renames a Volume Group

LVM Layer 3 – Logical Volumes, File Systems

lvcreate -L 10G vg1 – Create a 10GB logical volume on Volume Group vg1 lvchange and lvreduce - Typically not used lvrename – Rename Logical Volume lvremove – Removes a Logical Volume lvscan – Shows Logical Volumes lvdisplay – Shows details on Logical Volumes lvextend -l +100%FREE /dev/vg1/lv1 – Extend Logical Volume lv1 that takes up ALL of the remaining free space on the Volume Group vg1 resize2fs /dev/vg1/lv1 – Resize the file system to the size of the logical volume lv1