lvm usage cases

[karamelichkin]

Does anyone successfully use LVM as a storage device for their virtual machines?

`locals {
disk_sizes = {
"30GB" = 32212254720 # 30 * 1024^3
}

provider "libvirt" {
alias = "kvm3"
uri = "qemu+sshcmd://root@192.168.1.2/system"
}

resource "libvirt_pool" "st0_pool_kvm3" {
provider = libvirt.kvm3

name = "st0-storage"
type = "logical"

source = {
name = "st0"
}

target = {
path = "/dev/st0"
}
}

resource "libvirt_volume" "alpine_base_empty" {
provider = libvirt.kvm3

name = "alpine-3.22-base"
pool = libvirt_pool.st0_pool_kvm3.name
capacity = local.disk_sizes["30GB"]
}`

# lvs -a st0
  LV                         VG  Attr       LSize  Pool Origin                     Data%  Meta%  Move Log Cpy%Sync Convert
  alpine-3.22-base           st0 swi-a-s---  4.00m      [alpine-3.22-base_vorigin] 0.00                                   
  [alpine-3.22-base_vorigin] st0 ori-a-s--- 30.00g                                                                        

Is it possible to avoid using thin provisioning methods with LVM storage - not creating base images, snapshots. Use raw LVM instead, then perform necessary operations through Terraform null_resource?

[karamelichkin]

% terraform version
Terraform v1.12.2
on darwin_arm64

• provider registry.terraform.io/dmacvicar/libvirt v0.9.1
• provider registry.terraform.io/hashicorp/null v3.2.4

resource "libvirt_volume" "ubuntu-base" {
  provider = libvirt.kvm3

  name = "ubuntu-base"
  pool = libvirt_pool.st0_pool_kvm3.name
  format = "raw" 
  
  create = {
    content = {
      url = "https://cloud-images.ubuntu.com/releases/22.04/release/ubuntu-22.04-server-cloudimg-amd64.img"
    }
  }
}

then

terraform plan     
╷
│ Error: Unsupported argument
│ 
│   on terraform.tf line 62, in resource "libvirt_volume" "ubuntu-base":
│   62:   format = "raw" 
│ 
│ An argument named "format" is not expected here.

[karamelichkin]

I figured out that

resource "libvirt_volume" "st0_volume_kvm3" {
  provider = libvirt.kvm3
  
  name     = "vm-disk-01"
  pool     = libvirt_pool.st0_pool_kvm3.name
  capacity = local.disk_sizes["30GB"]
}

creates too small snapshot overlay

lvs -a
  LV                   VG  Attr       LSize  Pool Origin               Data%  Meta%  Move Log Cpy%Sync Convert
  vm-disk-01           st0 swi-a-s---  4.00m      [vm-disk-01_vorigin] 0.00                                   
  [vm-disk-01_vorigin] st0 ori-a-s--- 30.00g  

and another important thing is to run vm with lvm storages by terraform on latest debian host you needs to disable app armor for libvirt

ln -s /etc/apparmor.d/usr.sbin.libvirtd /etc/apparmor.d/disable/

without it terraform apply falls with output

│ Domain was defined but failed to start: internal error: process exited while connecting to monitor: 2025-12-06T12:06:15.633184Z qemu-system-x86_64: -blockdev
│ {"driver":"host_device","filename":"/dev/st0/vm-disk-01","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}: Could not open '/dev/st0/vm-disk-01':
│ Permission denied