Description

In Linux, Logical Volume Manager (LVM) is a device mapper target that provides logical volume management for the Linux kernel. LVM is used for the following purposes:

Creating single logical volumes of multiple physical volumes or entire hard disks (somewhat similar to RAID 0, but more similar to JBOD), allowing for dynamic volume resizing.
Managing large hard disk farms by allowing disks to be added and replaced without downtime or service disruption, in combination with hot swapping.
On small systems (like a desktop), instead of having to estimate at installation time how big a partition might need to be, LVM allows filesystems to be easily resized as needed.
Performing consistent backups by taking snapshots of the logical volumes.
Encrypting multiple physical partitions with one password.

LVM can be considered as a thin software layer on top of the hard disks and partitions, which creates an abstraction of continuity and ease-of-use for managing hard drive replacement, repartitioning and backup.

(source: WikiPedia)

Theory

Command's

Volume group

To view the free space of your volume group, or the physical storage, run vgdisplay. As you can see, I got 52GB in use and 170GB free.

root@scrat:~# vgdisplay 
  --- Volume group ---
  VG Name               scrat-vg
  System ID             
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  5
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                3
  Open LV               3
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               222.82 GiB
  PE Size               4.00 MiB
  Total PE              57042
  Alloc PE / Size       13436 / 52.48 GiB
  Free  PE / Size       43606 / <170.34 GiB
  VG UUID               e3grIy-rsTn-iUN6-Qpp2-wnnX-R2HP-s3BM7B

Logical volume

We can also see the logical volumes inside the volume group. This is the lvdisplay command. As you can see, the volume has a size of almost 9GB.

root@scrat:~# lvdisplay 
  --- Logical volume ---
  LV Path                /dev/scrat-vg/root
  LV Name                root
  VG Name                scrat-vg
  LV UUID                m5R02p-mx2h-gbTU-sWsv-n2n6-ov5b-Y8Y9f7
  LV Write Access        read/write
  LV Creation host, time scrat, 2020-04-23 18:34:58 +0200
  LV Status              available
  # open                 1
  LV Size                10.00 GiB
  Current LE             2216
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           254:1

Resize

You can resize the logical volume. You only change the partition size, not the formatting! The + is for the amount of data you want to add tothe volume. Without it's the total amount the volume has to become.

root@scrat:~# lvextend -L+5G /dev/scrat-vg/root
  Rounding size to boundary between physical extents: 4.90 GiB
  Size of logical volume centos/var changed from 10.00 GiB (1280 extents) to 15.00 GiB (2560 extents).
  Logical volume var successfully resized

Grow filesystem

To let the filesystem grow, online, use for ext3/4:

resize2fs /dev/scrat-vg/root

For xfs based filesystems:

xfs_growfs /dev/scrat-vg/root

Wiki

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