Problem encountered

I had a proxmox server locally running with a disk space of roughly 4TBs. The time came to analyze an unsually large disk image (~1TB). However, by default, when you install a proxmox server, two partitions are created: local and *local-lvm":

local is usually automatically assigned ~90-100GB, and this partition is where the root ("/") is mounted. local-lvm gets all the remaining space left on your server.

local is a regular directory, and thus you can store any files or folders you want there (containers’ and VM’s backup, IS files, etc..). On the other hand, local-lvm is a volume used to efficiently manage and allocate disk space. It is in local-lvm that you will see your lists of VMs and containers (that’s where they are stored). You can’t add files/folders in this partition as you would on “local”.

To create a VM from a backup disk image in promox, you first need to upload it to the proxmos server. However, I had less than 100GB available on the server (and my backup image was ~1TB).

Solution

I had to reduce the space assigned to local-lvm and hand it over to “local”. P.S. This involves recreating local-lvm to a smaller size. Thus, in the process, you will lose all the VMs and containers previously created (since they are all stored on local-lvm).

Steps

Before we dive in, let’s log in to our proxmox server and have a quick look at the space assigned to local and local-lvm:

root@pve1:~# lvs
  LV     VG   Attr         LSize  Pool Origin       Data%  Meta%  Move Log Cpy%Sync Convert
  data   pve  twi-aotz--   4.00t                    0.22   10.55                           
  root   pve  -wi-ao----  <96G                                                                                  
  swap   pve  -wi-ao----   8.00g

As you can see, my root file system is of size < 96G.

1. We need to remove the data volume (local-lvm):

root@pve1:~# lvremove /dev/pve/data
Do you really want to remove active logical volume pve/data? [y/n]: y
 Logical volume \"data\" successfully removed

2. We can now create a smaller volume for data. Let’s assign 3TB to it (instead of the initial 4TB):

root@pve1:~# lvcreate -L 3000G -n data pve
  Logical volume \"data\" created

3. We need to convert the created data volume to a thin pool:

root@pve1:~# lvconvert --type thin-pool pve/data
Thin pool volume with chunk size 64.00 KiB can address at most 15.81 TiB of data.
  WARNING: Converting pve/data to thin pool\'s data volume with metadata wiping.
  THIS WILL DESTROY CONTENT OF LOGICAL VOLUME (filesystem etc.)
Do you really want to convert pve/data? [y/n]: y
  Converted pve/data to thin pool.

4. We now tell Proxmox to forget about the current local-lvm storage. That’s, we will remove the current local-lvm and add the newly created one:

root@pve1:~# pvesm remove local-lvm

root@pve1:~# pvesm add lvmthin local-lvm -thinpool data -vgname pve -content rootdir, images

There is now more free space in the volume group (which we will use to expand the root filesystem):

root@pve1:~# vgs
 VG  #PV #LV #SN Attr   VSize  VFree
 pve   1   7   0 wz--n- 4.36T  1.20t

5. We may now expand the root file system by 1TB:

root@pve1:~# lvextend -L +1000g /dev/pve/root
  Size of logical volume pve/root changed from 96 GiB to 1096 GiB.
  Logical volume pve/root successfully resized.

6. The filesystem of my root directory was ext. However, since its size was increased, we need to spread that filesystem throughout the newly added space:

root@pve1:~# resize2fs /dev/mapper/pve-root

If yours was XFS instead of ext, you should use this:

root@pve1:~# xfs_growfs /dev/mapper/pve-root

That’s it! You may check the new sizes of the logical volume “data” and the root directory “/root”

root@pve1:~# lvs
  LV    VG  Attr        LSize  Pool Origin       Data%  Meta%  Move Log Cpy%Sync Convert
  data  pve twi-aotz--  3.00t                    0.22   10.55                           
  root  pve -wi-ao---- <1.27t                                                           
  swap  pve -wi-ao----  8.00g  

Kudos to wiki.wevers.tv whose material I used to make this post.