How to Expand a Disk in a Linux (VM): Step-by-Step Guide

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Expanding a disk in a virtual machine is a common task for system administrators. This blog demonstrates how to increase a disk size from 30 GB to 100 GB, scan for the new size, and expand the associated logical volume. We’ll use the following steps:

  • Initial disk size: 30 GB
  • Target disk size: 100 GB
  • Hostnames and setup: We’ll use a hostname vmhost01 for illustration.

Step 1: Verify Existing Disk Configuration

Before making any changes, inspect the current disk setup.

Commands:

# List physical volumes with their associated devices
pvs -o+devices

# Display block devices
lsblk

Example Output:

[root@vmhost01 ~]# pvs -o+devices
  PV         VG     Fmt  Attr PSize    PFree Devices     
  /dev/sda6  vg00   lvm2 a--    60.00g    0  /dev/sda6(0)
  /dev/sdb   vg_app lvm2 a--  <130.00g    0  /dev/sdb(0)
  /dev/sdc   vg00   lvm2 a--   <30.00g    0  /dev/sdc(0)

[root@vmhost01 ~]# lsblk
NAME            MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda               8:0    0   70G  0 disk 
├─sda1            8:1    0  512M  0 part /boot
├─sda2            8:2    0    4G  0 part [SWAP]
└─sda6            8:6    0   60G  0 part 
  └─vg00-root   253:0    0   60G  0 lvm  /
sdc               8:32   0   30G  0 disk 
  └─vg00-root   253:0    0   30G  0 lvm  /

Step 2: Rescan the Disk

After increasing the disk size in your VM’s hypervisor, the OS must rescan the disk to detect the new size.

Command:

echo 1 > /sys/block/sdc/device/rescan

Verify the Change:

lsblk

Example Output:

[root@vmhost01 ~]# lsblk
NAME            MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdc               8:32   0  100G  0 disk 
  └─vg00-root   253:0    0   30G  0 lvm  /

Step 3: Resize the Physical Volume

Next, resize the physical volume (/dev/sdc) to reflect the new size.

Command:

pvresize /dev/sdc

Verify the Updated Size:

pvs -o+devices

Example Output:

[root@vmhost01 ~]# pvs -o+devices
  PV         VG     Fmt  Attr PSize   PFree Devices     
  /dev/sdc   vg00   lvm2 a--  100.00g 40.00g /dev/sdc(0)

Step 4: Extend the Logical Volume

With the physical volume resized, extend the logical volume.

Commands:

# Extend the logical volume
lvextend -l +100%FREE /dev/vg00/root

# Resize the filesystem
resize2fs /dev/vg00/root

Example Output:

[root@vmhost01 ~]# lvextend -l +100%FREE /dev/vg00/root
  Size of logical volume vg00/root changed from 60.00 GiB to 100.00 GiB.

[root@vmhost01 ~]# resize2fs /dev/vg00/root
resize2fs 1.45.6 (20-Mar-2020)
Filesystem at /dev/vg00/root is mounted on /; on-line resizing required
The filesystem on /dev/vg00/root is now 100G.

Step 5: Verify the Expansion

Finally, confirm the logical volume and filesystem have been expanded.

Commands:

lsblk
df -h

Example Output:

[root@vmhost01 ~]# lsblk
NAME            MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdc               8:32   0  100G  0 disk 
  └─vg00-root   253:0    0  100G  0 lvm  /

[root@vmhost01 ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg00-root 100G   10G   90G  10% /

Using these steps, we successfully expanded a disk from 30 GB to 100 GB, ensuring the logical volume and filesystem utilized the additional space. This procedure can be adapted to other environments with different configurations.

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