Hello,
after some (much) fiddling, I managed to boot a VM with two (LVM) mirrored root disks over iSCSI with both libiscsi (User_Mode_iSCSI) and kernel iSCSI.
I'm using other Proxmox nodes in the cluster as LIO targets.
BTW: please fix iscsi-login-negotiation-failed - I skipped the tcp_ping in...