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

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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:
GNU/Linux | Disk partition scheme

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

Increase disk size

VMware

VMware Logo

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:
VMware | Modify disk size
  • The virtual disk now looks as follows:
GNU/Linux | Disk partition scheme

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

Ubuntu

Ubuntu Logo

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:
GNU/Linux | Disk partition scheme
  • 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:
GNU/Linux | Disk partition scheme

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:
GNU/Linux | Disk partition scheme
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:
GNU/Linux | Disk partition scheme
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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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