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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.  There may be a limit of 16 characters on the password).
  • 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 server/target

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 client/initiator

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.  Starting the daemon will generate error messages because there's no configuration yet.

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.

Using the iSCSI-provided block device

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 

Normal operations

In normal operations the client/initiator should be shut down before the server/target.  Doing otherwise will result in a delayed shutdown by the client/initiator.

Issue investigation

How to identify which /dev/sd[a-z]+ are iSCSI devices

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

ls -l /dev/disk/by-path/ | grep 'ip-.*iqn\.'

If lshw is installed, more information is available by

lshw -class disk -class storage

hdparm doesn't work on iSCSI devices.  When smartctl was tried there was a server/target kernel abort task for iSCSI target.

Error messages

iscsiadm: initiator reported error (19 - encountered non-retryable iSCSI login failure)

As the messages suggest, an authentication failure.  Check user name and password consistency between server/target and client/initiator.

 


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