Expand Ubuntu 20 Proxmox Disk

README.md

# Resize the file system in UI, under VM -> Hardware -> Click on the disk to resize, click "Resize disk" button

# Confirm increase in disk space (1TB in my case)
$ lsblk
NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                         8:0    0    1T  0 disk
├─sda1                      8:1    0    1M  0 part
├─sda2                      8:2    0    1G  0 part /boot
└─sda3                      8:3    0    1T  0 part
  └─ubuntu--vg-ubuntu--lv 253:0    0   31G  0 lvm  /

# Resize the partition
$ sudo parted /dev/sda
GNU Parted 3.3
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print
Warning: Not all of the space available to /dev/sda appears to be used, you can fix the GPT to use all of the space (an extra 629145600 blocks) or continue with the current setting? 
Fix/Ignore? Fix 
Model: QEMU QEMU HARDDISK (scsi)
Disk /dev/sda: 1000GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  2097kB  1049kB                     bios_grub
 2      2097kB  1076MB  1074MB  ext4
 3      1076MB  31.0GB  30.0GB

(parted) resizepart 3 100%
(parted) quit
Information: You may need to update /etc/fstab.

# Resize the physical volume
$ sudo pvresize /dev/sda3
  Physical volume "/dev/sda3" changed
  1 physical volume(s) resized or updated / 0 physical volume(s) not resized

# Extend the logical volume now
$ sudo lvextend -r -l +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv
  Size of logical volume ubuntu-vg/ubuntu-lv changed from <31.00 GiB (7935 extents) to 1.03 TiB (270079 extents).
  Logical volume ubuntu-vg/ubuntu-lv successfully resized.
resize2fs 1.45.5 (07-Jan-2020)
Filesystem at /dev/mapper/ubuntu--vg-ubuntu--lv is mounted on /; on-line resizing required
old_desc_blocks = 4, new_desc_blocks = 132
The filesystem on /dev/mapper/ubuntu--vg-ubuntu--lv is now 276560896 (4k) blocks long.

# Confirm resize complete
$ lsblk
NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda                         8:0    0    1T  0 disk
├─sda1                      8:1    0    1M  0 part
├─sda2                      8:2    0    1G  0 part /boot
└─sda3                      8:3    0    1T  0 part
  └─ubuntu--vg-ubuntu--lv 253:0    0    1T  0 lvm  /