VM disks on local-lvm thin not thin provisioning

[eds89]

Hi,

I have two PVE nodes with the default loval-lvm storage, which is an lvm-thin storage type. As far as I'm aware, this supports thin provisioning.

I have a set of three VMs on each node, which should be using pretty much the same amount of storage on each node.
One is FreeBSD, one is Linux Ubuntu and one is Windows.
The FreeBSD and Linux VMs have 40G disks, and the Windows has 100G.
Qemu agent enabled on all three, with guest trim enabled. Disks have discard enabled.

On one node, I can see all three VMs are using about 40GB of space total on local-lvm. On the other node, they are using about 160GB.
If I move the Windows VM as an example to my ZFS over iSCSI storage, the created zvol is 40GB, but if I move it back to the local-lvm, it consumes the full 100GB.
There is definitely not 100GB of data on the disk within the VM, and I have used sdelete to zero out all free space within Windows.

What I'm trying to understand is;

1. Why are the three VMs using more storage on one node than the other
2. Why is the disk using the full 100GB on the local-lvm if thin provisioning is enabled
3. How can I perform some action to trim the disk on the local-lvm so that I am using the same amount of storage on each node
4. In Linux, is there an equivalent process to zero out free space

Any guidance appreciated.

Thanks
Eds