Using Ansible to automate Logical Volume Manager configurations

Ansible is an automation, configuration, and infrastructure management tool. My previous articles introduce Ansible and explain system roles.  In this article, I demonstrate configuring Logical Volume Manager (LVM) using Ansible. Configuring LVM with Ansible helps system administrators perform their tasks more efficiently and spend less time working manually. You can create an Ansible playbook that creates a partition and initializes LVM.

[ You might also enjoy: Introduction to Logical Volume Manager ]

LVM Overview

As you know, the primary partition can't be extended and reduced. Such a scenario can create problems when you need extra space on a disk. Using LVM, you can overcome this problem because LVM lets you add and remove a new disk to a logical volume. LVM is part of the default installation of Red Hat Enterprise Linux (RHEL) since RHEL 7.

Here are a few essential items you need to understand before using LVM:

• PV—Physical Volume initialized on disk, partition, or loopback file. When you initialize a PV, it creates a label at the start of the device.
• VG—Volume Group is a collection of logical volumes (LVs). You create a VG inside a PV.
• LV—Logical Volume is just like a standard partition on a disk. You can create multiple LVs inside a single VG. You can resize an LV according to the space required.

Creating a Partition

In RHEL 8, you create a partition using the Parted utility. Parted gives you the flexibility to create a partition using MS-DOS or a GUID Partition Table (GPT) partition. In Ansible, you can use the Parted module for partitioning.

In this example, consider /dev/vdb as the disk name. Create two 1 GB partitions.  Simply using the Parted module, you can create partitions of any size.

Example:

---
- name: playbook for simple 1 GB partition
  hosts: vm1.example.com
  become: true
  tasks:
    - name: create partition
      parted:
        device: /dev/vdb
        number: 1
        flags: [ lvm ]
        state: present
        part_end: 2GB

Run this playbook using:

$ ansible-playbook partition.yml

You can use the lsblk command to check that the partition now exists. 

Initializing LVM and creating  LVs

After creating the partition, initialize the LV. To initialize requires you to first create both a PV and a VG. Use the Ansible lvg module to create a PV and a VG with a Physical Extents (PE) size. The PE divides the VG into a fixed size. By default, the size of the PE is 4MB. You can change the default size while creating the VG. Generally, a larger PE size provides better performance.

Example:

- name: task for creating volume group
  lvg:
      vg: sample-vg
      pvs: /dev/vdb1
      pesize: 16

- name: Install lvm2 dependency
  package:
    name: lvm2
    state: present

The next task creates the LV. The lvol module creates LVs.  When creating an LV, you give options like VG name, size, and an LV name.

In this example, a 2GB VG creates the first LV with a size of 1GB.

Example:

- name: task for creating logical volume
  lvol:
      vg: sample-vg
      lv:  sample-lv
      size: 1g
      force: yes

To use this created LV, you have to mount that partition within the filesystem.  Only you can access this LV for storing data. In Ansible, use the filesystem modules for formatting any block device with filesystem. After formatting, you mount the partition at any directory. You can use the mount module in Ansible. Make sure that the directory (/data1 in this example) exists before executing the playbook.

Example:

 - name: Create directory data1 if does not exist
      file:
        path: /data1
        state: directory
        mode: '0755'
- name: format the xfs filesystem
  filesystem:
    fstype: xfs
    dev: /dev/sample-vg/sample-lv
- name: mount the lv on /data1
  mount:
    path: /data1
    src: /dev/sample-vg/sample-lv
    fstype: xfs
    state: mounted

Example: Whole playbook: 

---
- name: playbook for simple 1 GB partition
  hosts: localhost
  become: true
  tasks:
    - name: create partition
      parted:
        device: /dev/nvme1n1
        number: 1
        flags: [ lvm ]
        state: present
        part_end: 2GB

    - name: Install lvm2 dependency
      package:
        name: lvm2
        state: present

    - name: task for creating volume group
      lvg:
          vg: sample-vg
          pvs: /dev/nvme1n1p1
          pesize: 16

    - name: task for creating logical volume
      lvol:
          vg: sample-vg
          lv:  sample-lv
          size: 1g
          force: yes

    - name: Create directory data1 if does not exist
      file:
        path: /data1
        state: directory
        mode: '0755'

    - name: format the xfs filesystem
      filesystem:
        fstype: xfs
        dev: /dev/sample-vg/sample-lv

    - name: mount the lv on /data1
      mount:
        path: /data1
        src: /dev/sample-vg/sample-lv
        fstype: xfs
        state: mounted

Run this playbook and check whether your LV gets created or use the lvs command.

Remember that one of the features of LVM is that you can extend the size of the LV. Manually, you can use the lvextend command. In Ansible, you can use the lvol module to extend the size of sample-lv.

Example:

- name: Extend the logical volume to take all remaining space of the PVs and resize the underlying filesystem
  lvol:
      vg: sample-vg
      lv: sample-lv
      size: 2g
      resizefs: true
      force: yes

Using the lvextend command or the lvol module helps you to extend your LV. In this lvol volume, use the resizefs parameter to enlarge an unmounted file system located on the device. 

In order to shrink the size of an LV, the syntax is as follows:

- name: Extend the logical volume to take all remaining space of the PVs and resize the underlying filesystem
      lvol:
          vg: sample-vg
          lv: sample-lv
          size: 700m
          shrink: yes
          force: yes

[ Need more on Ansible? Take a free technical overview course from Red Hat. Ansible Essentials: Simplicity in Automation Technical Overview. ] 

Wrap Up

This article showed you how to configure LVM using a simple Ansible playbook. Rather than using a simple playbook, you could create a role, using the same process and modules as above. Ansible helps you reduce manual tasks as well as increase efficiency for LVM configuration. Using the methods described in this article simplifies operations on multiple managed nodes.