Manage and configure LVM storage

Welcome to our comprehensive guide on managing and configuring LVM (Logical Volume Manager) storage in Linux. LVM is a powerful tool that provides storage flexibility by allowing you to combine free space from different parts of a disk—or even from multiple disks—into a single continuous partition as seen by the operating system. With LVM, you can easily resize storage partitions, making it convenient to expand capacity as your needs grow.

In this guide, you will explore various LVM operations, including creating physical volumes, volume groups, and logical volumes, as well as resizing and formatting them. Most CentOS installations come with LVM tools pre-installed. If your system does not have them, install the package with:

sudo dnf install lvm2

For demonstration purposes, assume that three new virtual disks, each with 5 gigabytes of capacity, have been added to your virtual machine.

Key LVM Concepts

Before diving into the commands, it is essential to understand the core LVM terminology:

• PV (Physical Volume): A real storage device such as an entire disk or a partition.
• VG (Volume Group): A collection (or pool) of physical volumes that creates a single virtual disk.
• LV (Logical Volume): A partition created within a volume group.
• PE (Physical Extent): The basic unit into which a physical volume is subdivided.

Viewing Available Physical Volumes

A Physical Volume (PV) represents a real storage device. To display all available PVs and check which ones are used by LVM, execute:

sudo lvmdiskscan

You might see output similar to:

[aaron@LFCS-CentOS ~]$ sudo lvmdiskscan
[sudo] password for aaron:
/dev/sda1    [  1.00 GiB]
/dev/sda2    [ <19.00 GiB] LVM physical volume
/dev/sdb1    [  4.00 GiB]
/dev/sdb2    [  4.00 GiB]
/dev/sdb3    [ <2.00 GiB]
/dev/sdc     [  5.00 GiB]
/dev/sdd     [  5.00 GiB]
/dev/sde     [  5.00 GiB]
3 disks
4 partitions
0 LVM physical volume whole disks
1 LVM physical volume
[aaron@LFCS-CentOS ~]$

In this output, /dev/sda2 is already configured as an LVM physical volume (likely set up during the CentOS installation), so it will be excluded from further operations in this lesson.

Creating Physical Volumes

To incorporate new storage, designate two of the new disks (for example, /dev/sdc and /dev/sdd) as physical volumes:

sudo pvcreate /dev/sdc /dev/sdd

A successful output will look like:

[aaron@LFCS-CentOS ~]$ sudo pvcreate /dev/sdc /dev/sdd
  Physical volume "/dev/sdc" successfully created.
  Physical volume "/dev/sdd" successfully created.
[aaron@LFCS-CentOS ~]$

Verify the current physical volumes with:

sudo pvs

Expected output:

[aaron@LFCS-CentOS ~]$ sudo pvs
  PV         VG       Fmt  Attr PSize  PFree 
  /dev/sda2  cs       lvm2 a-- <19.00g    0 
  /dev/sdc   lvm2     ---   5.00g  5.00g 
  /dev/sdd   lvm2     ---   5.00g  5.00g 
[aaron@LFCS-CentOS ~]$

The PFree column shows the free storage available on each physical volume.

Creating a Volume Group

To utilize the available storage, create a Volume Group (VG) that aggregates the physical volumes into one virtual disk. For example, combining /dev/sdc and /dev/sdd creates a VG of 10 gigabytes. Create the volume group named "my_volume" with:

sudo vgcreate my_volume /dev/sdc /dev/sdd

Output confirmation:

[aaron@LFCS-CentOS ~]$ sudo vgcreate my_volume /dev/sdc /dev/sdd
Volume group "my_volume" successfully created
[aaron@LFCS-CentOS ~]$

Extending a Volume Group

If you require additional storage, you can extend the volume group. First, create a physical volume on a new disk (e.g., /dev/sde):

sudo pvcreate /dev/sde

Next, extend your volume group with:

sudo vgextend my_volume /dev/sde

Then verify the updated volume group details using:

sudo vgs

A sample output might be:

[aaron@LFCS-CentOS ~]$ sudo vgs
 VG         #PV #LV #SN Attr       VSize  VFree 
 cs         1   2  0 wz--n  <19.00g     0 
 my_volume  3   0  0 wz--n  <14.99g <14.99g
[aaron@LFCS-CentOS ~]$

sudo vgreduce my_volume /dev/sde
sudo pvremove /dev/sde

Creating Logical Volumes

Once the physical volumes and volume group are ready, create Logical Volumes (LVs) to act as partitions within the VG.

Create a logical volume named "partition1" with a size of 2GB in "my_volume":

sudo lvcreate --size 2G --name partition1 my_volume

Expected output:

[aaron@LFCS-CentOS ~]$ sudo lvcreate --size 2G --name partition1 my_volume
Logical volume "partition1" created.
[aaron@LFCS-CentOS ~]$

Check the volume groups to view logical volumes and available free space:

sudo vgs

Sample output:

[aaron@LFCS-CentOS ~]$ sudo vgs
  VG         #PV #LV #SN Attr     VSize   VFree 
  cs         1   2  0  wz--n- <19.00g      0 
  my_volume  2   1  0  wz--n-  9.9g    7.99g
[aaron@LFCS-CentOS ~]$

You may also create a second logical volume (e.g., "partition2") with a size of 6GB:

sudo lvcreate --size 6G --name partition2 my_volume

Verify with:

sudo lvs

Which might output:

[aaron@LFCS-CentOS ~]$ sudo lvs
LV           VG         Attr       LSize   Pool Origin Data% Meta% Move Log Cpy%Sync Convert
root         cs         -wi-a---- <17.00g
swap         cs         -wi-a---- 2.00g
partition1   my_volume  -wi-a---- 2.00g
partition2   my_volume  -wi-a---- 6.00g
[aaron@LFCS-CentOS ~]$

And for a final check:

sudo vgs

Example:

[aaron@LFCS-CentOS ~]$ sudo vgs
VG          #PV #LV #SN Attr     VSize   VFree
cs          1   2   0  wz--n  <19.00g    0
my_volume   2   2   0  wz--n  9.99g  1.99g
[aaron@LFCS-CentOS ~]$

Resizing Logical Volumes (LVs)

Growing a Logical Volume

Data in an LV is divided into physical extents (PEs). To expand an LV to utilize all available extents in its volume group, run:

sudo lvresize --extents 100%VG my_volume/partition1

A sample output might be:

Reducing 100%VG to remaining free space 3.99 GiB in VG.
Size of logical volume my_volume/partition1 changed from 2.00 GiB (512 extents) to 3.99 GiB (1022 extents).
Logical volume my_volume/partition1 successfully resized.

Shrinking a Logical Volume

To reduce a logical volume to a specific size (for example, 2GB), use:

sudo lvresize --size 2G my_volume/partition1

This command will warn you about potential data loss. If you are sure, confirm the reduction:

WARNING: Reducing active logical volume to 2.00 GiB.
THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce my_volume/partition1? [y/n]: y
Size of logical volume my_volume/partition1 changed from 3.99 GiB (1022 extents) to 2.00 GiB (512 extents).
Logical volume my_volume/partition1 successfully resized.

Creating a Filesystem on a Logical Volume

An LV must be formatted with a filesystem before it becomes useful. For instance, to format "partition1" with the XFS filesystem, run:

sudo mkfs.xfs /dev/my_volume/partition1

The output will confirm the creation of the new XFS filesystem along with details such as metadata and block sizes.

Resizing an LV with an Existing Filesystem

If your logical volume includes a filesystem, you need to resize both the LV and the filesystem concurrently. XFS supports online expansion (but cannot be shrunk while mounted). To expand "partition1" from 2GB to 3GB, run:

sudo lvresize --resizefs --size 3G my_volume/partition1

An example output sequence:

Size of logical volume my_volume/partition1 changed from 2.00 GiB (512 extents) to 3.00 GiB (768 extents).
Logical volume my_volume/partition1 successfully resized.
meta-data=/dev/mapper/my_volume-partition1 isize=512 agcount=4, agsize=131072 blks
...
data blocks changed from 524288 to 786432

Note that while many filesystems can expand online, they generally cannot be shrunk without unmounting.

Viewing Logical Volume Details

To display detailed information about your logical volumes, use:

sudo lvdisplay

This command shows details such as the LV path, name, size, status, and more. An example output for "partition1" might be:

--- Logical volume ---
LV Path                /dev/my_volume/partition1
LV Name                partition1
VG Name                my_volume
LV UUID                EIlInFA-hqqM-F9Sp-3F7m-oPte-hElc-jRx4vN
LV Write Access        read/write
LV Creation host, time LFCS-CentOS, 2022-03-24 17:37:40 -0500
LV Status              available
# open                 0
LV Size                2.00 GiB
Current LE             512
Segments               1
Allocation             inherit
Read ahead sectors     auto (currently set to 8192)
Block device           253:2

This LV path (/dev/my_volume/partition1) works in a similar way to standard device files like /dev/vda.

Additional LVM Commands and Tips

If you ever need help or a quick refresher on any LVM command, refer to the manual pages by running:

man lvm

While navigating the manual, you can use tab-completion in the terminal. For example, type "vg" and press Tab twice to see available VG options such as:

• vgcreate
• vgdisplay
• vgexport
• vgchange
• vgck
• vgextend
• vgimport
• vgmerge
• vgimportdevices
• vgcfgrestore
• vgmknodes
• vgreduce
• vgs
• vgsplit

This concludes our guide on managing and configuring LVM storage in Linux. Armed with these commands and tips, you are now ready to explore further lab exercises and enhance your Linux storage management skills.