Proxmox iSCSI multipath is what you want when a single network link to your TrueNAS box isn’t enough. Two NICs, two switches, one LUN — if a cable dies, storage keeps working. Here’s the config that actually worked for me.
TrueNAS side: create the target
First, make sure you have a zvol or file extent ready. Then go to Sharing > Block Shares (iSCSI). Add a target, give it a name like truenas-multipath. Under Portal, add two portals — one on each NIC’s IP. If your TrueNAS has 10.0.0.10 and 10.0.1.10, list both. Then create an extent pointing to your zvol, and associate it with the target. Leave the LUN ID at 0 unless you have a reason.
Proxmox initiator: install and discover
On the Proxmox host, install open-iscsi if it’s not already there:
apt install open-iscsiThen discover the targets from both portals:
iscsiadm -m discovery -t st -p 10.0.0.10
iscsiadm -m discovery -t st -p 10.0.1.10You should see the same target IQN listed twice. That’s fine — it’s the same LUN behind two paths.
Multipath config
Now enable multipath. Edit /etc/multipath.conf and make sure it has a defaults section with find_multipaths yes. Then restart multipathd:
systemctl restart multipath-toolsCheck that the device shows up as multipath:
multipath -llYou should see a device like mpath0 with two paths, both active. If you only see one path, check that both portals are reachable and that the IQN matches exactly.
Add storage to Proxmox
In the Proxmox GUI, go to Datacenter > Storage > Add > iSCSI. Enter the portal IP (use one of them), and it should auto-detect the target. Select it, and Proxmox will create a storage entry. For multipath, make sure the storage is set to use the multipath device, not a single path. You can verify by checking /dev/mapper/mpath0 exists.
Failover test
This is the part everyone skips. Pull one of the network cables from the Proxmox host. Wait a few seconds, then check multipath -ll again. One path should show failed, the other still active. Your VM storage keeps working. Plug the cable back in, and the path should recover automatically. I did this on my own setup and it worked as expected — no I/O errors, no dropped VMs.
One thing: if you’re using a single switch for both NICs, you’re not really testing much. Use two separate switches or at least two VLANs to make the test meaningful.
If you’re already using TrueNAS for other stuff, check out Proxmox with arr stack in LXC: a working setup with TrueNAS mounts — it covers the NFS/SMB side of things.
