1. Find the ZFS Dataset Path

Use the zfs list command to find your container's dataset. Replace 114 with your container number:

zfs list | grep 114

The output will include a line similar to this, confirming the path:

NAME                           USED  AVAIL  REFER  MOUNTPOINT
Tank/subvol-114-disk-0          2.5T   500G   2.5T  /Tank/subvol-114-disk-0

2. Check the Mount Point on the Host

The ZFS subvolume is actually mounted directly on the Proxmox host, usually at a path that matches the ZFS path:

mount | grep subvol-114-disk-0

3. Reducing the Size

Since the pct resize command failed, proceed with the manual method using the path Tank/subvol-114-disk-0:

  1. Stop the Container: pct stop 114

  2. Manually Set Quota: zfs set refquota=1800G Tank/subvol-114-disk-0

  3. Update Config File: Edit /etc/pve/lxc/114.conf to change size=2900G to size=1800G.

  4. Start Container: pct start 114

Note: I was having issues earlier by specifying 1.8T instead of using 1800G for the disk size parameter. Your mileage may vary depending on Proxmox version.