How do I shrink my Proxmox VM disk?

Comments

• tridinebandim OG

  January 3

  Something something convert to qcow then resize lmresize something something

  Thats all i remember 😅

  Thanked by (1)Freek
• itsdeadjim

  January 3 edited January 3

  1 TiB = 2⁴⁰ = 1024GiB
  1 TB = 10¹² = 1000GB
  7.3 TiB ≈ 8TB

  I don't use proxmox/lvm but general rule is to first resize the filesystem within the virtual disk and then touch the disk.
  Since it's very easy to mess things up, resize filesystem and then export it to a new disk.

  What's the filesystem inside the vm?

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• Freek Senpai

  January 3

  @itsdeadjim said:
  1 TiB = 2⁴⁰ = 1024MB
  1 TB = 10¹² = 1000MB
  7.3 TiB ≈ 8TB

  I don't use proxmox/lvm but general rule is to first resize the filesystem within the virtual disk and then touch the disk.
  Since it's very easy to mess things up, resize filesystem and then export it to a new disk.

  What's the filesystem inside the vm?

  Thanks for the tip. Filesystem inside the VM is ext4.

  LinuxFreek.com
• itsdeadjim

  January 3 edited January 3

  Great, go with something like gparted to check the inner filesystem and shrink it as low as possible (5.3tb) then lvreduce on the host to resize the vm-..-disk-0 to something like 6-7TB (or whatever) and then again with gparted to expand the inner filesystem to fill the remaining space. Double check if this procedure aligns with proxmox best practices because I dont use it.

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• itsdeadjim

  January 3

  I see that lvreduce also has --resizefs option to shrink also the underlying filesystem, but I think it's riskier.

  Thanked by (1)Freek
• Falzo Senpai

  January 3 edited January 3

  Like @itsdeadjim wrote, first shrink the filesystem within the VM. Also the partition it is on!
  Don't use --resizefs with lvreduce from the outside.

  It usually is a good idea to run fstrim inside the vm beforehand and do the fs and partition shrinking from a rescue cd/gparted.

  Check if it boots up after those shrinking steps, only then reduce the actual device with lvreduce while the VM is stopped.

  You probably also want to adjust the config file of proxmox to reflect the size change properly.

  Leave gaps/breathing room esp. if unsure with the units ;-)

  Thanked by (4)itsdeadjim localhost Freek wankel
• Freek Senpai

  January 4 edited January 4

  Thanks for the pointers @Falzo and @itsdeadjim . Seems like I was really close during my initial approach, but the key for me was to verify the disk and fix any issues using gdisk after resizing it (as shown below).

  For future reference (and because people who write "I fixed it" and don't post the solution go to hell): The goal of the steps below is to resize the ext4 partition /dev/sda2 and its disk /dev/sda to 6.9T, so that they fit within the thin-LVM pool sized at 6.95T (as shown in the opening post).

  ⚠️ Disclaimer: I have no idea what I'm doing, so follow these steps at your own risk.

  ---

  Steps:

  1. Trim Unused Space

  Inside the VM, run:

  fstrim -a
  

  This will save time during the disk operations.

  ---

  2. Boot into GParted Live ISO

  Boot the VM using the GParted Live ISO.

  ---

  3. Resize the Partition

  Use the GParted GUI to shrink the partition /dev/sda2 to the smallest size possible, leaving a little headroom.
  Example:
  

  ---

  4. Shutdown the VM

  After resizing, the partition /dev/sda2 will now be smaller, but the disk itself (/dev/sda) will still be the original size. Let's fix that. Shut down the VM.
  Example:
  

  ---

  5. Resize the Disk on the Proxmox Host

  On the Proxmox host (hypervisor), resize the VM disk to fit within the thin-LVM pool:

  lvreduce -L 6.9T /dev/media/vm-101-disk-0
  

  Replace /dev/media/vm-101-disk-0 with your VM's disk path.

  Why 6.9T? My thin-LVM is 6.95T, so I left a bit of headroom to avoid overcommitting the pool.
  Example:
  

  ---

  6. Rescan the Disk in Proxmox

  Run the following to make Proxmox aware of the new disk size:

  qm rescan
  

  Example output:
  

  ---

  7. Attempt to Boot the VM

  If you're lucky, the VM will boot without issues. However, you'll most likely encounter an error like:

  ALERT! /dev/disk/by-uuid/xxxxxxxxx does not exist. Dropping to a shell
  

  If this happens, boot the VM into the GParted Live ISO again. The GParted GUI will show all storage as unallocated, but don’t panic (famous last words).
  Example:
  

  ---

  8. Fix Partition Errors with gdisk

  Open a terminal in GParted and run:

  sudo gdisk /dev/sda
  

  • Type v to verify the disk.

  • You’ll likely see warnings or errors. Follow the on-screen instructions to fix them.

    • For example, I had to go to the expert menu (x), then press e, and so on, until all errors were resolved.

  • Once everything is fixed, type w to write the changes to the disk and press Enter.
    Example:
    

  ---

  9. Resize the Partition Back to Match the Disk

  Open the GParted GUI again. This time, you can expand the partition to fill the resized disk.
  Example:
  

  ---

  10. Verify the Disk Layout

  Check that the disk size and partition size match your desired configuration:

  sudo fdisk -l
  

  Example:
  

  ---

  11. Check the Filesystem for Errors

  Run a filesystem check to ensure no errors:

  e2fsck -f /dev/sda2
  

  ---

  12. Reboot the VM

  Finally, reboot the VM. It should boot without any issues, and the disk and partition should now be sized as desired.
  Example:
  

  ---

  That wasn't so hard after all… lol. I hope it helps

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• yoursunny OG

  January 4

  @Freek said:
  people who write "I fixed it" and don't post the solution go to hell

  ☑️

  Thanked by (5)Ympker Freek wankel Decicus dfroe

  No hostname left!
• Ympker OGContent WriterSenpai

  January 4

  @Freek said:
  Thanks for the pointers @Falzo and @itsdeadjim . Seems like I was really close during my initial approach, but the key for me was to verify the disk and fix any issues using gdisk after resizing it (as shown below).

  For future reference (and because people who write "I fixed it" and don't post the solution go to hell): The goal of the steps below is to resize the ext4 partition /dev/sda2 and its disk /dev/sda to 6.9T, so that they fit within the thin-LVM pool sized at 6.95T (as shown in the opening post).

  ⚠️ Disclaimer: I have no idea what I'm doing, so follow these steps at your own risk.

  ---

  Steps:

  1. Trim Unused Space

  Inside the VM, run:

  fstrim -a
  

  This will save time during the disk operations.

  ---

  2. Boot into GParted Live ISO

  Boot the VM using the GParted Live ISO.

  ---

  3. Resize the Partition

  Use the GParted GUI to shrink the partition /dev/sda2 to the smallest size possible, leaving a little headroom.
  Example:
  

  ---

  4. Shutdown the VM

  After resizing, the partition /dev/sda2 will now be smaller, but the disk itself (/dev/sda) will still be the original size. Let's fix that. Shut down the VM.
  Example:
  

  ---

  5. Resize the Disk on the Proxmox Host

  On the Proxmox host (hypervisor), resize the VM disk to fit within the thin-LVM pool:

  lvreduce -L 6.9T /dev/media/vm-101-disk-0
  

  Replace /dev/media/vm-101-disk-0 with your VM's disk path.

  Why 6.9T? My thin-LVM is 6.95T, so I left a bit of headroom to avoid overcommitting the pool.
  Example:
  

  ---

  6. Rescan the Disk in Proxmox

  Run the following to make Proxmox aware of the new disk size:

  qm rescan
  

  Example output:
  

  ---

  7. Attempt to Boot the VM

  If you're lucky, the VM will boot without issues. However, you'll most likely encounter an error like:

  ALERT! /dev/disk/by-uuid/xxxxxxxxx does not exist. Dropping to a shell
  

  If this happens, boot the VM into the GParted Live ISO again. The GParted GUI will show all storage as unallocated, but don’t panic (famous last words).
  Example:
  

  ---

  8. Fix Partition Errors with gdisk

  Open a terminal in GParted and run:

  sudo gdisk /dev/sda
  

  • Type v to verify the disk.

  • You’ll likely see warnings or errors. Follow the on-screen instructions to fix them.

    • For example, I had to go to the expert menu (x), then press e, and so on, until all errors were resolved.

  • Once everything is fixed, type w to write the changes to the disk and press Enter.
    Example:
    

  ---

  9. Resize the Partition Back to Match the Disk

  Open the GParted GUI again. This time, you can expand the partition to fill the resized disk.
  Example:
  

  ---

  10. Verify the Disk Layout

  Check that the disk size and partition size match your desired configuration:

  sudo fdisk -l
  

  Example:
  

  ---

  11. Check the Filesystem for Errors

  Run a filesystem check to ensure no errors:

  e2fsck -f /dev/sda2
  

  ---

  12. Reboot the VM

  Finally, reboot the VM. It should boot without any issues, and the disk and partition should now be sized as desired.
  Example:
  

  ---

  That wasn't so hard after all… lol. I hope it helps

  I actually keep a wiki on GitHub with server tasks I've done to remember how to accomplish them again, in case I forget. Awesome that you keep this documented

  Thanked by (1)Freek

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• terrorgen OG

  January 4

  This warrants a blog post for future reference.

  Thanked by (2)AuroraZero esyede

  The all seeing eye sees everything...
• esyede

  January 4 edited January 4

  @terrorgen said:
  This warrants a blog post for future reference.

  +1 for this.
  Might need it in the future
• Freek Senpai

  January 4

  Thanks for the feedback, I appreciate it. I could probably spin up a demo VM and go through over all the steps again in a video or something for a blog (?).

  @Ympker said:
  I actually keep a wiki on GitHub with server tasks I've done to remember how to accomplish them again, in case I forget. Awesome that you keep this documented

  Haha recognizable. I use my 'note to self' blog for cases like this

  LinuxFreek.com