Disk Type Support For iSCSI

H

happycow

New Member
Apr 1, 2026
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I attached an iSCSI Target to my node
Created LVM from it
They are shared between my 3 Proxmox nodes

I cloned a VM from NFS to this LVM over iSCSI
It took qcow2 as the format.

I tried some API GET queries to fetch the disk info

The VM is on n1
Code: 
curl -k -H 'Authorization: PVEAPIToken=<token>' "https://<ip>:8006/api2/json/nodes/pve-n1/storage/iSCSI-VM-Storage/content/iSCSI-VM-Storage:vm-104-disk-0.qcow2"

{
  "data": {
    "used": 0,
    "path": "/dev/iscsi_vg_01/vm-104-disk-0.qcow2",
    "format": "qcow2",
    "size": 53687091200
  }
}

Ran the same query to n2
Code: 
curl -k -H 'Authorization: PVEAPIToken=<token>' "https://<ip>:8006/api2/json/nodes/pve-n2/storage/iSCSI-VM-Storage/content/iSCSI-VM-Storage:vm-104-disk-0.qcow2"

{
  "data": null,
  "message": "volume_size_info on 'iSCSI-VM-Storage:vm-104-disk-0.qcow2' failed - no format\n"
}

Then I converted them to RAW and it works for the same query to all nodes
Code: 
{
  "data": {
    "format": "raw",
    "size": 53699674112,
    "used": 0,
    "path": "/dev/iscsi_vg_01/vm-104-disk-0"
  }
}

https://pve.proxmox.com/pve-docs/pve-admin-guide.html#_storage_types
From this I see for block storage "Allows to store large raw images. "

I was concerned that we allowed to create qcow2 but we don't support it?
 
When you enable "Allow Snapshots as Volume-Chain", Proxmox switches the disk format from raw to qcow2 to leverage the qcow2-based snapshot mechanism on block storage.

Since standard LVM on iSCSI/Fibre Channel does not natively support snapshots in a way that Proxmox can easily manage across multiple nodes, this new Tech Preview for Proxmox 9 creates a qcow2 volume chain on top of the LVM block device. This allows you to have the performance of iSCSI combined with the flexibility of qcow2 snapshots.

As shown in the architecture below, Proxmox layers the QCOW2 image directly onto the Logical Volume (LV):

2026-04-01_17-37.png

For more details on how this "Volume-Chain" implementation works, these articles provide a great deep dive:
 
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