apt update && apt install open-iscsi
nano /etc/iscsi/iscsid.conf

set startup to automatic in /etc/iscsi/iscsid.conf

# To request that the iscsi service scripts startup a session, use "automatic":
# node.startup = automatic
#
# To manually startup the session, use "manual". The default is manual.
node.startup = automatic

iscsiadm --mode node session --targetname iqn.2004-04.com.qnap:ts-435xeu:iscsi.target-0.965df6 --portal 10.52.12.13:3260 --login
iscsiadm --mode session -P 3
gdisk /dev/sdb
mkfs.ext4 /dev/sdb1
mkdir /mnt/backup
blkid
mount UUID=d6ed961a-717e-404b-9d8c-71cea8ecda04 /mnt/backup

/etc/fstab

UUID=d6ed961a-717e-404b-9d8c-71cea8ecda04 /mnt/backup ext4 _netdev 0 0

iscsiadm --mode node --targetname iqn.2004-04.com.qnap:ts-435xeu:iscsi.target-0.965df6 --portal 10.52.12.13:3260 --login    # login
iscsiadm --mode node --targetname iqn.2004-04.com.qnap:ts-435xeu:iscsi.target-0.965df6 --portal 10.52.12.13:3260 --logout   # logout