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

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

# *************
# CHAP Settings
# *************

# To enable CHAP authentication set node.session.auth.authmethod
# to CHAP. The default is None.
#
# NOTE: currently this attribute is checked for validity but then
# ignored, so even if it is set to None, CHAP will be used if the
# credentials (username/password and possibly username_in/password_in)
# are set. This behavior is deprecated, and in the future CHAP will
# not be used if authmethod is set to None.
#
node.session.auth.authmethod = CHAP

# To configure which CHAP algorithms to enable, set
# node.session.auth.chap_algs to a comma separated list.
# The algorithms should be listed in order of decreasing
# preference - in particular, with the most preferred algorithm first.
# Valid values are MD5, SHA1, SHA256, and SHA3-256.
# The default is MD5.
#node.session.auth.chap_algs = SHA3-256,SHA256,SHA1,MD5

# To set a CHAP username and password for initiator
# authentication by the target(s), uncomment the following lines:
node.session.auth.username = initiator-iscsi
node.session.auth.password = <12-16 alphanumeric>

# To set a CHAP username and password for target(s)
# authentication by the initiator, uncomment the following lines:
node.session.auth.username_in = target-iscsi
node.session.auth.password_in = <12-16 alphanumeric>

iscsiadm --mode discovery -t sendtargets --portal 10.52.12.13:3260
iscsiadm --mode node --targetname iqn.2004-04.com.qnap:ts-435xeu:iscsi.target-0.965df6 --portal 10.52.12.13:3260 --login
iscsiadm --mode session -P 3
fdisk -l
gdisk /dev/sdb1
fdisk -l
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

create datastore on pbs

proxmox-backup-manager datastore create remote-iscsi /mnt/backupnas

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