LVM: Difference between revisions

Latest revision as of 07:15, 4 September 2024

The Logical Volume Manager (LVM) provides means to dynamically organize partitions.

Basic Setup

LVM manages three types:

physical volumes - directly on a physical partition
volume groups - a group of physical volumes
logical volumes

Create a logical volume

# 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 Logical Volume

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 Logical Volumes 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 16: / Line 16: @@
 # creates a new logical volume named "home" with the size of 10GB (check with lvdisplay)
 # makes /dev/pool/home available
-lvcreate -L 10G -n home pool
+lvcreate --size 10G --name home pool
 mkfs.ext4 /dev/pool/home
 </syntaxHighlight>
 === Use the Logical Volume ===
-in your `configuration.nix`:
+in your <code>configuration.nix</code>:
 <syntaxHighlight lang=nix>
@@ Line 29: / Line 29: @@
 };
 </syntaxHighlight>
-== 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 to put into your <code>configuration.nix</code>:
+== 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>:
 <syntaxHighlight lang=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
 </syntaxHighlight>
@@ Line 45: / Line 49: @@
 === Disko ===
-Disko provides means to automatically generate the creation and configuration of logical volumes, see http://cgit.lassul.us/disko/tree/README.md .
+Disko provides means to automatically generate the creation and configuration of logical volumes, see https://github.com/nix-community/disko