This post merges both A little follow up on this post and Increasing Disk Size on Existing VM and fixes a couple of mistakes.

First off, go to your Proxmox host. Run the resize command:


qm resize <vmid> <disk> <size>
where vmid is the ID in your VM ID, disk is the identifier of the disk inside the VM, it’s most likely to be scsi0. size is the size you want to add or remove, something like +100G or +1T is both valid.

Now go into your VM, run the following command to check if the system has notices a disk resize:


dmesg | grep sda
Where sda is the disk, it could be vda or sdb.

Run the following command to get your disk and display the partitions, remember to change sda if required.


fdisk -l /dev/sda | grep ^/dev
Remember the number of the partition you want to increase, it’s most likely the biggest one.

Run the following command to open parted with the drive:


parted /dev/sda

Run a list to check if everything is recognized correctly and run the following command:


resizepart <partition number, integer only> 100%
You could change the 100% to add only a percentage of the free space and add the remaining space to another partition, but to keep it simple we’ll give it all to this partition.

If it asks to fix the unused space type F to fix it, if it asks for a partition number and size; just put in the values like above.

Ctrl-C out of Parted and run df -h, you’ll notice that you still do not have your extra space! Run pvresize /dev/<block> to start resizing, remember to subsitute <block> with your partition like sda3.

Now run lvextend -l +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv and resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv to actually resize your LVM partition. Remember to replace /dev/mapper/ubuntu--vg-ubuntu--lv with your LVM partition, you can find it by running df -h and looking for the one mounted on /.

That’s it! The drive has been expanded and readily available, no need to reboot!

Sources:
https://pve.proxmox.com/wiki/Resize_disks