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Introduction

This page summarises configuring iSCSI on Debian 6 and 7.  Thanks to HowtoForge's excellent "Using iSCSI On Debian Squeeze (Initiator And Target)" from which most of the information was learned.

Overview

iSCSI allows a server to provide a virtual block device over a network to a client.  The virtual block device can then be treated like a real block device – for example it can be partitioned and file systems created in the partitions.

In iSCSI terminology the server is a "target" and the client is an "initiator".  On this page they are called server/target and client/initiator.

Links

Planning

You will need:

  • A user name and password (for the iSCSI configuration so a free choice)
  • A server/target computer:
    • root access
    • The IP address.  If there is more than one, the one that will be used by the client/initiator to access it.
    • A local block device to be made available to the initiator (client) via iSCSI.  May be a file, a HDD (whole device or partition), an LVM volume or a RAID device.
  • A client/initiator computer
    • root access

Setting up the target (server)

Installation

aptitude -y install iscsitarget iscsitarget-dkms

Configuration

Optionally backup the configuration files that will be changed: /etc/default/iscsitarget and /etc/iet/ietd.conf.

sed -i 's/ISCSITARGET_ENABLE=false/ISCSITARGET_ENABLE=true/' /etc/default/iscsitarget

The next step sets up to serve a single LVM volume, /dev/vg0/lv0.  Values that need to be changed are red.  The user and password values are need when configuring the client/initiator.  Values that are arbitrary strings (so could be changed) are in blue.

user=someone
password=secret
local_device=/dev/vg0/lv0

oIFS=$IFS; array=($(hostname --long)); IFS=$oIFS
for ((i=${#array[*]};i>0;i--)); do backwards_fqdn+=.${array[i-1]}; done

( echo "Target iqn.$(date +%Y-%m)$backwards_fqdn:storage.lun0"
    echo "    IncomingUser $user $password"
    echo "    OutgoingUser"
    echo "    Lun 0 Path=$local_device,Type=fileio"
    echo "    Alias LUN0"
) > /etc/iet/ietd.conf

It can be useful to know the Target value just created when configuring the client/initiator.  It can be displayed with

head -1 /etc/iet/ietd.conf

Further devices can be added by editing /etc/iet/ietd.conf, replicating and modifying the first stanza.

Setting up the initiator (client)

Installation

aptitude -y install open-iscsi

Configuration

Optionally backup the configuration file that will be changed: /etc/iscsi/iscsid.conf.

sed -i 's/node.startup = manual/node.startup = automatic/' /etc/iscsi/iscsid.conf

In the next step, the iSCSI daemon is used to generate an initial configuration.  Values that need to be changed are red. 

target_ip=192.168.10.27
/etc/init.d/open-iscsi restart
iscsiadm -m discovery -t st -p $target_ip

This should create a sub-directory of /etc/iscsi/nodes/ with the same name as the Target created when configuring the server/target.

Within that sub-directory there should be a further sub-directory with name beginning with the server/target's IP address.

Note: if the server/target has two IP address (accessible by the client/initiator?) there will be two such sub-sub-directories.  It may be possible to configure a client/initiator to work this way but initial explorations did not identify how to do so.  In this case, delete the sub-sub-directory for the IP address you do not want to use.

In the next step, the user name and password are added to the configuration.

Change to the new /etc/iscsi/nodes/<target>/<IP address ...> directory.  In the commands below, the sed command should be on a single line.

user=someone
password=secret
sed -i "s/^node.session.auth.authmethod = None$/node.session.auth.authmethod = CHAP\nnode.session.auth.username = $user\nnode.session.auth.password = $password/" default

Testing

/etc/init.d/open-iscsi restart

The output should include:

Login to [iface: default, target: <target>, portal: <ip address>,<port>]: successful

and a new /dev/sd[a-z]+ device file should have appeared.

Further configuration

The new /dev/sd[a-z]+ block device can be configured as desired.

If it is configured with file system(s) to be mounted at boot there are special considerations for /etc/fstab:

  • LABEL or UUID must be used.  This is in case the /dev/sd[a-z]+ name assigned by udev changes from boot to boot.
  • The options must include _netdev.  This ensures that mounting is deferred until the networking daemons (including open-iscsi) are running.
  • The sixth field (fs_passno) must be set to 0.  This disables fsck when mounting via fstab, necessary because it does not work.

If fscking is required ... TODO 

Issue investigation

How to identify a /dev/sd[a-z]+ as an iSCSI device

The easiest way is to list /dev/disk/by-path/

If lshw is installed, more information is available by

lshw -class disk -class storage

hdparm doesn't work. 

When smartctl was tried there was a kernel iSCSI target abort task on the target/initiator.


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