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GNU/Linux - How to increase the size of a disk without interrupting service

Last updated: Oct 13, 2024

I had a virtual machine running Ubuntu whose disk I needed to extpand because my /var partition was full.

I challenged myself and wanted to do it live, i.e. without downtime.

⚠️ Modifying the partition table can lead to data loss. It is therefore important to make a full backup of your machine before making any changes.⚠️

VM Configuration

Virtual machine properties

OS: Ubuntu Server 20.04 LTS
Disk: 80G
Partitionning scheme: GPT
Partitions: LVM
Hypervisor: VMware 6.7

Virtual disk

To get a graphical representation, my virtual hard drive looked like this:

As explained, the problem was that my /var partition was full and I had to extend it.

Increase disk size

VMware

First, we need to expand the virtual disk. In this example, I'm going to increase my virtual disk by 20G with 4G dedicated to my /var partition. I'll keep the remaining 16G as a reserve for the future.

From VMware or any other hypervisor, increase the virtual disk size. Here, I'm going from 60G to 80G:

The virtual disk now looks as follows:

⚠️ Just in case, I recommend taking a snapshot of the Virtual Machine at this stage.⚠️

Ubuntu

gdisk

As we can see with gdisk tool, the modification is not automatically taken into account:

user@ubuntu:~$ sudo gdisk -l /dev/sda
GPT fdisk (gdisk) version 1.0.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 125829120 sectors, 60.0 GiB
odel: Virtual disk    
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): 76AC5877-F92F-4C0E-BC53-504F7E90466A
Partition table holds up to 128 entries
ain partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 125829086
Partitions will be aligned on 2048-sector boundaries
Total free space is 4029 sectors (2.0 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         1050623   512.0 MiB   EF00  
   2         1050624         3147775   1024.0 MiB  8300  
   3         3147776       125827071   58.5 GiB    8300

For the new size to be taken into account by the system, we need to perform a disk scan:

user@ubuntu:~$ echo 1 | sudo tee /sys/block/sda/device/rescan

Still using the gdisk tool, we can check that our new disk size has been taken into account. Note also the starting sector of the sda3 partition:

user@ubuntu:~$ sudo gdisk -l /dev/sda
GPT fdisk (gdisk) version 1.0.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 167772160 sectors, 80.0 GiB
odel: Virtual disk    
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): 76AC5877-F92F-4C0E-BC53-504F7E90466A
Partition table holds up to 128 entries
ain partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 125829086
Partitions will be aligned on 2048-sector boundaries
Total free space is 4029 sectors (2.0 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         1050623   512.0 MiB   EF00  
   2         1050624         3147775   1024.0 MiB  8300  
   3         3147776       125827071   58.5 GiB    8300

Before making any changes, we need to rewrite our secondary gpt header:

user@ubuntu:~$ sudo gdisk /dev/sda
GPT fdisk (gdisk) version 1.0.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): w
Warning! Secondary header is placed too early on the disk! Do you want to
correct this problem? (Y/N): Y

Have moved second header and partition table to correct location.

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/sda.
Warning: The kernel is still using the old partition table.
The new table will be used at the next reboot or after you
run partprobe(8) or kpartx(8)
The operation has completed successfully.

Check free space:

user@ubuntu:~$ sudo gdisk -l /dev/sda
GPT fdisk (gdisk) version 1.0.5

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 167772160 sectors, 80.0 GiB
odel: Virtual disk    
Sector size (logical/physical): 512/512 bytes
Disk identifier (GUID): 76AC5877-F92F-4C0E-BC53-504F7E90466A
Partition table holds up to 128 entries
ain partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 167772126
Partitions will be aligned on 2048-sector boundaries
Total free space is 41947069 sectors (20.0 GiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         1050623   512.0 MiB   EF00  
   2         1050624         3147775   1024.0 MiB  8300  
   3         3147776       125827071   58.5 GiB    8300

At this point, Ubuntu should see the virtual disk like this:

We can now use gdisk to extend the sda3 partition to its new size:
- d: we fist delete partition 3
- n: we then create a new partition 3 with new boundaries (sector 3147776 to 167772126)

user@ubuntu:~$ sudo gdisk /dev/sda

Command (? for help): d
Partition number (1-3): 3

Command (? for help): n
Partition number (3-128, default 3): 3
First sector (34-125829086, default = 3147776) or {+-}size{KMGTP}: 3147776
Last sector (3147776-125829086, default = 167772126) or {+-}size{KMGTP}: 
Current type is 8300 (Linux filesystem)
Hex code or GUID (L to show codes, Enter = 8300): 
Changed type of partition to 'Linux filesystem'

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/sda.
Warning: The kernel is still using the old partition table.
The new table will be used at the next reboot or after you
run partprobe(8) or kpartx(8)
The operation has completed successfully.

Use the partprobe command to make the kernel take the new partition table into account:

user@ubuntu:~$ sudo partprobe

At this point, Ubuntu should see the virtual disk like this:

LVM

Physical Volume

With pvdisplay, we can see that our physical volume needs to be resized:

user@ubuntu:~$ sudo pvdisplay /dev/sda3
  --- Physical volume ---
  PV Name               /dev/sda3
  VG Name               ubuntu-vg
  PV Size               <58.50 GiB / not usable 2.00 MiB
  Allocatable           yes (but full)
  PE Size               4.00 MiB
  Total PE              14975
  Free PE               0
  Allocated PE          14975
  PV UUID               ThZ9VT-3zCa-SQrB-6s9a-ZiWL-DbqP-TqRNxM

Run pvresize to extend the physical volume:

user@ubuntu:~$ sudo pvresize /dev/sda3
  Physical volume "/dev/sda3" changed
  1 physical volume(s) resized or updated / 0 physical volume(s) not resized

Run pvdisplay to check that volume has been resized correctly:

user@ubuntu:~$ sudo pvdisplay /dev/sda3
  --- Physical volume ---
  PV Name               /dev/sda3
  VG Name               ubuntu-vg
  PV Size               <78.50 GiB / not usable 1.98 MiB
  Allocatable           yes (but full)
  PE Size               4.00 MiB
  Total PE              20095
  Free PE               5120
  Allocated PE          14975
  PV UUID               ThZ9VT-3zCa-SQrB-6s9a-ZiWL-DbqP-TqRNxM

From Ubuntu perspective, the virtual disk now looks like this:

Logical Volume

Last but not least, we now need to resize our /var partition.

We can resize the logical volume and the ext4 partition in a single command with lvextend:
- -r: resizefs, Resize underlying filesystem together with the LV
- -L+4G: add 4G to the ubuntu--vg-lvvar logical volume

user@ubuntu:~$ sudo lvextend -r -L+4G /dev/mapper/ubuntu--vg-lvvar 
  Size of logical volume ubuntu-vg/lvvar changed from 4.00 GiB (1024 extents) to 8.00 GiB (2048 extents).
  Logical volume ubuntu-vg/lvvar successfully resized.
resize2fs 1.45.5 (07-Jan-2020)
Filesystem at /dev/mapper/ubuntu--vg-lvvar is mounted on /var; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 1
The filesystem on /dev/mapper/ubuntu--vg-lvvar is now 2097152 (4k) blocks long.

That's it, the size of /var is now 8G:

user@ubuntu:~$ df -h | grep var
/dev/mapper/ubuntu--vg-lvvar	7.9G  5.3G  2.2G  71% /var

From Ubuntu side the virtual disk now looks like this: