LVM: Difference between revisions

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[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.

<~~syntaxHighlight~~ lang=~~bash~~>

=== Create an LV ===

# ~~formats~~ the partion into a physical volume (check with pvdisplay)

Below are shell commands to setup a PV, a VG and an LV from scratch. LVM comes enabled by default on NixOS.<syntaxhighlight lang="shell">

# format the partion into a physical volume (check with pvdisplay)

pvcreate /dev/sda2

# ~~creates~~ a new volume group named pool (check with vgdisplay)

# create 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)

# create 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

# finally, create a filesystem inside the logical volume

mkfs.ext4 /dev/pool/home

</~~syntaxHighlight~~>

</syntaxhighlight>

=== Use the ~~Logical Volume~~ ===

=== Use the LV ===

~~in your <code>configuration~~.~~nix</code>:~~

Mount the filesystem on the logical volume by adding an entry to the {{Nixos:option|fileSystems}} NixOS option.

{{File|3=fileSystems."/home" = {

~~<syntaxHighlight lang~~=~~nix>~~

fileSystems."/home" = {

device = "/dev/pool/home";

fsType = "ext4";

};

};|name=/etc/nixos/configuration.nix|lang=nix}}

</~~syntaxHighlight>~~

== 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 Nixpkgs issue {{Issue|33646}}). Here is a non-exhaustive list of features and the corresponding kernel module and other options to put into your NixOS configuration:

~~<syntaxHighlight lang~~=~~nix>~~

boot.initrd.kernelModules = [

{{File|3=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`

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];

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

services.lvm.boot.thin.enable = true; # when using thin provisioning or caching|name=/etc/nixos/configuration.nix|lang=nix}}

</~~syntaxHighlight>~~

== Automated Partitioning ==

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=== 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]]

@@ 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.
-<syntaxHighlight lang=bash>
+=== Create an LV ===
-# formats the partion into a physical volume (check with pvdisplay)
+Below are shell commands to setup a PV, a VG and an LV from scratch. LVM comes enabled by default on NixOS.<syntaxhighlight lang="shell">
+# format the partion into a physical volume (check with pvdisplay)
 pvcreate /dev/sda2
-# creates a new volume group named pool (check with vgdisplay)
+# create 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)
+# create 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
+# finally, create a filesystem inside the logical volume
 mkfs.ext4 /dev/pool/home
-</syntaxHighlight>
+</syntaxhighlight>
-=== Use the Logical Volume ===
+=== Use the LV ===
-in your <code>configuration.nix</code>:
+Mount the filesystem on the logical volume by adding an entry to the {{Nixos:option|fileSystems}} NixOS option.
+{{File|3=fileSystems."/home" = {
-<syntaxHighlight lang=nix>
-fileSystems."/home" = {
    device = "/dev/pool/home";
    fsType = "ext4";
-};
+};|name=/etc/nixos/configuration.nix|lang=nix}}
-</syntaxHighlight>
 == 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 Nixpkgs issue {{Issue|33646}}). Here is a non-exhaustive list of features and the corresponding kernel module and other options to put into your NixOS configuration:
-<syntaxHighlight lang=nix>
-boot.initrd.kernelModules = [
+{{File|3=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`
@@ Line 40: / Line 39: @@
 ];
-services.lvm.boot.thin.enable = true; # when using thin provisioning or caching
+services.lvm.boot.thin.enable = true; # when using thin provisioning or caching|name=/etc/nixos/configuration.nix|lang=nix}}
-</syntaxHighlight>
 == Automated Partitioning ==
@@ Line 47: / Line 45: @@
 === 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]]