LVM: Difference between revisions

Revision as of 11:29, 10 February 2026

Linux's Logical Volume Manager (LVM) provides means to dynamically organize partitions. For example, partitions can be created, moved, resized and deleted regardless of fragmentation on disk.

Basic Setup

LVM manages four basic building blocks:

Physical volume (PV): Unix block device node reserved for use by LVM. Examples: a disk partition, a whole disk (i.e. without a partition table), a meta device, or a loopback file.
Volume group (VG): Group of PVs for allocating PEs to LVs.
Logical volume (LV): "Virtual partition" composed of PEs inside a VG.
Physical extent (PE): The smallest contiguous extent (default 4 MiB) in the physical volume that can be allocated to an LV.

Create an LV

# formats the partion into a physical volume (check with pvdisplay)
pvcreate /dev/sda2
# creates a new volume group named pool (check with vgdisplay)
vgcreate pool /dev/sda2
# creates a new logical volume named "home" with the size of 10GB (check with lvdisplay)
# makes /dev/pool/home available
lvcreate --size 10G --name home pool
mkfs.ext4 /dev/pool/home

Use the LV

in your configuration.nix:

fileSystems."/home" = {
  device = "/dev/pool/home";
  fsType = "ext4";
};

Booting with special LVM Modes

LVM provides a number of special features such as creating snapshots, RAID for single LVs and much more. If you want to use these devices on bootup, the associated dm-* kernel module must be provided in the initrd (see for example 🚩︎#33646). This is a non-exhaustive list of features and the corresponding kernel module and other options to put into your configuration.nix:

boot.initrd.kernelModules = [
  "dm-snapshot" # when you are using snapshots
  "dm-raid" # e.g. when you are configuring raid1 via: `lvconvert -m1 /dev/pool/home`
  "dm-cache-default" # when using volumes set up with lvmcache
];

services.lvm.boot.thin.enable = true; # when using thin provisioning or caching

Automated Partitioning

People have created a number of tools to automate the partitioning in NixOS:

NixOps

NixOps can repartition Hetzner Physical Machines, see NixOps Manual.

Disko

Disko provides means to automatically generate the creation and configuration of logical volumes, see https://github.com/nix-community/disko

@@ Line 1: / Line 1: @@
-[https://en.wikipedia.org/wiki/Logical_Volume_Manager_(Linux) The Logical Volume Manager] (LVM) provides means to dynamically organize partitions.
+Linux's '''[https://en.wikipedia.org/wiki/Logical_Volume_Manager_(Linux) Logical Volume Manager] (LVM)''' provides means to dynamically organize partitions. For example, partitions can be created, moved, resized and deleted regardless of fragmentation on disk.
 == Basic Setup ==
-LVM manages three types:
-; Physical volume (PV) : Space reservation consisting of a disk partition, a whole disk, a meta device, or a loopback file.
+LVM manages four basic building blocks:
-; Volume group (VG) : Group of physical volumes.
-; Logical volume (LV) : Space reservation inside a volume group, which may be laid across multiple physical volumes.
-=== Create a logical volume ===
+; Physical volume (PV) : Unix block device node reserved for use by LVM. Examples: a disk partition, a whole disk (i.e. without a partition table), a meta device, or a loopback file.
+; Volume group (VG) : Group of PVs for allocating PEs to LVs.
+; Logical volume (LV) : "Virtual partition" composed of PEs inside a VG.
+; Physical extent (PE) : The smallest contiguous [[wikipedia:Extent (file systems)|extent]] (default 4 MiB) in the physical volume that can be allocated to an LV.
+=== Create an LV ===
 <syntaxHighlight lang=bash>
@@ Line 21: / Line 23: @@
 </syntaxHighlight>
-=== Use the Logical Volume ===
+=== Use the LV ===
 in your <code>configuration.nix</code>:
@@ Line 32: / Line 34: @@
 == Booting with special LVM Modes ==
-LVM provides a number of special features such as creating snapshots, raid for single Logical Volumes and much more. If you want to use these devices on bootup, the associated <code>dm-*</code>  kernel module must be provided in the initrd (see for example {{Issue|33646}}) . This is a non-exhaustive list of features and the corresponding kernel module and other options to put into your <code>configuration.nix</code>:
+LVM provides a number of special features such as creating snapshots, RAID for single LVs and much more. If you want to use these devices on bootup, the associated <code>dm-*</code> kernel module must be provided in the initrd (see for example {{Issue|33646}}). This is a non-exhaustive list of features and the corresponding kernel module and other options to put into your <code>configuration.nix</code>:
 <syntaxHighlight lang=nix>
 boot.initrd.kernelModules = [
@@ Line 47: / Line 49: @@
 === NixOps ===
-NixOps can repartition Hetzner Physical Machines, see [[https://nixos.org/nixops/manual/#idm140737318354032 NixOps Manual]].
+NixOps can repartition Hetzner Physical Machines, see [https://nixos.org/nixops/manual/#idm140737318354032 NixOps Manual].
 === Disko ===
 [[Disko]] provides means to automatically generate the creation and configuration of logical volumes, see https://github.com/nix-community/disko
+== See also ==
+* [https://wiki.archlinux.org/title/LVM The corresponding ArchWiki page]
 [[Category:Filesystem]]