Introduction¶

If you have a NAS in your network, it can be convinient to setup iSCSI on the NAS and export logical drives to your Debian server. This HOWTO has been tested on Debian Wheezy.

Package that need to be installed¶

# apt-get install open-iscsi

On the target (NAS)¶

In this example we use XEN on our Debian server and we use iSCSI for the different drive partitions on the virtual machines (DomU's).

Create one target in the NAS for every virtual machine and one LUN on the target for every partition the virtual machine will use e g disk and swap.

On the initiator (Debian server running XEN)¶

Configure udev rules¶

Run the following as root:

# echo 'KERNEL=="sd*", ACTION=="add", PROGRAM="/etc/udev/scripts/iscsidev.sh %p",SYMLINK+="iscsi/%c{1}/lun%c{2}"' > /etc/udev/rules.d/55-openiscsi.rules

# mkdir /etc/udev/scripts

# cat > /etc/udev/scripts/iscsidev.sh << EOF
#!/bin/sh

# FILE: /etc/udev/scripts/iscsidev.sh

BUS="\`echo "\$1" | sed 's/\//\n/g' | egrep '^[0-9]+:'\`"
HOST=\${BUS%%:*}

[ -e /sys/class/iscsi_host ] || exit 1

file="/sys/class/iscsi_host/host\${HOST}/device/session*/iscsi_session*/session*/targetname"

target_name=\$(cat \${file})

# This is not an open-scsi drive
if [ -z "\${target_name}" ]; then
    exit 1
fi

# Check if QNAP drive
check_qnap_target_name=\${target_name%%:*}
if [ \$check_qnap_target_name = "iqn.2004-04.com.qnap" ]; then
    target_name=\`echo "\${target_name%.*}"\`
fi

lun="\`echo \$BUS | awk -F: '{print \$NF}'\`" 

echo "\${target_name##*.} \$lun"
EOF

# chmod 755 /etc/udev/scripts/iscsidev.sh

Commands to use¶

To find targets from the NAS on the initiator (Debian server)
iscsiadm --mode discovery --type sendtargets --portal <TARGET_IP>

It is useful to use this command after a new target has been added on the NAS to get the target name.

Manually connect to a target
iscsiadm --mode node --targetname <TARGET> --portal <TARGET_IP>:3260 --login

Example
iscsiadm --mode node --targetname iqn.2004-04.com.qnap:ts-412:iscsi.dhcpserver.d8a009 --portal 192.168.1.1:3260 --login

Manually disconnect from a target
iscsiadm --mode node --targetname <TARGET> --portal <TARGET_IP>:3260 --logout

Tell open iscsi to automatically connect to a target during boot
iscsiadm --mode node --targetname <TARGET> --portal <TARGET_IP> --op update --name node.startup --value automatic

IMPORTANT NOTE
Your automatic settings will be reverted to manual everytime you perform a scan using
iscsiadm --mode discovery --type sendtargets

It might be a good idea to create a script where you configure your targets startup to be automatic. This script can be executed manually when needed.

/usr/local/bin/update-iscsi-targets.sh

#!/bin/sh
#

# Update targets will set start mode to manual
iscsiadm --mode discovery --type sendtargets --portal 192.168.1.1

# Set each target to automatic manually to specify the IP you want (multplie IPs on same NAS)
iscsiadm --mode node --targetname iqn.2004-04.com.qnap:ts-412:iscsi.dhcpserver.d8a009 --portal 192.168.1.1:3260 --op update --name node.startup --value automatic

The result¶

Your imported devices should now be available in /dev/iscsi/<TARGET_NAME>/<LUN>

Example
/dev/iscsi/dhcpserver/lun0

You can use the dives directly in your cfg file for your DomU or setup encryption with cryptsetup.