The iSCSI target configuration exports existing block devices or file system images to iSCSI initiators. First create the needed block devices with YaST or create file system images. For an overview of partitioning, see Section 8.5.7, “Using the YaST Partitioner”. File system images must be created manually. For example, if you want to create the image /var/lib/xen/images/xen-0 with the size 4GB, first make sure that the directory is there then create the image itself:

mkdir -p /var/lib/xen/images
dd if=/dev/zero of=/var/lib/xen/images/xen-0 seek=1M bs=4096 count=1

To configure the iSCSI target, run the iSCSI Target module in YaST. The configuration is split into three tabs. In the Service tab, select the start mode and the firewall settings. If you want to access the iSCSI target from a remote machine, select Open Port in Firewall. If a iSNS server should manage the discovery and access control, activate iSNS Access Control and enter the IP address of your iSNS Server. Note, that you cannot use even valid hostnames, but must use the IP address. For more about iSNS, read Chapter 13, iSNS for Linux Overview.

The Global tab provides settings for the iSCSI server. The authentication set here is used for the discovery of services, not for accessing the targets. If you do not want to restrict the access to the discovery, use No Authentication.

If authentication is needed, there are two possibilities to consider. One is that an initiator must prove that it has the permissions to run a discovery on the iSCSI target. This is done with Incoming Authentication. The other is that the iSCSI target must prove to the initiator that it is the expected target. Therefore, the iSCSI target can also provide a username and password. This is done with Outgoing Authentication. Find more information about authentication in RFC 3720 (see http://www.ietf.org/rfc/rfc3720.txt).

The targets are defined in the Targets tab. Use Add to create a new iSCSI target. The first dialog asks for information about the device to export.

The next menu configures the access restrictions of the target. The configuration is very similar to the configuration of the discovery authentication. In this case, at least an incoming authentication should be setup.

Next finishes the configuration of the new target, and brings you back to the overview page of the Target tab. Activate your changes by clicking on Finish.

Configure an iSCSI target in /etc/ietd.conf. All parameters in this file before the first Target declaration are global for the file. Authentication information in this portion has a special meaning—it is not global, but is used for the discovery of the iSCSI target.

If you have access to an iSNS server, the first thing to configure is telling the target about this server. Note, that the address of the iSNS server must always be given as IP address. A normal domain name is not sufficient. The configuration for this functionality looks like the following:

iSNSServer 192.168.1.111
iSNSAccessControl no

This configuration makes the iSCSI target register itself with the iSNS server, which in turn provides the discovery for initiators. For more about iSNS read Chapter 13, iSNS for Linux Overview. Note that the access control for the iSNS discovery is not supported. Just keep iSNSAccessControl no.

All direct iSCSI authentication may be done in two directions. The iSCSI target can require the iSCSI initiator to authenticate with the IncomingUser, which can be added multiple times. The iSCSI initiator may also require the iSCSI target to authenticate. Use OutgoingUser for this. Both have the same syntax:

IncomingUser <username> <password>
OutgoingUser <username> <password>

The authentication is followed by one or several target definitions. For each target, add a Target section. This section always starts with a Target identifier followed by definitions of logical unit numbers:

Target iqn.yyyy-mm.<reversed domain name>[:identifier]
          Lun 0 Path=/dev/mapper/system-v3
          Lun 1 Path=/dev/hda4
          Lun 2 Path=/var/lib/xen/images/xen-1,Type=fileio

In the Target line, yyyy-mm is the date when this target is activated, and identifier is freely selectable. Find more about naming conventions in RFC 3722 (see http://www.ietf.org/rfc/rfc3722.txt). Three different block devices are exported in this example. The first one is a logical volume (see also Section 7.1, “LVM Configuration”), the second is an IDE partition, and the third is an image available in the local file system. All these look like block devices to an iSCSI initiator.

Before activating the iSCSI target, add at least one IncomingUser after the Lun definitions. It does the authentication for the use of this target.

To activate all your changes, restart the iscsitarget daemon with rcopen-iscsi restart. Check your configuration in the /proc file system:

cat /proc/net/iet/volume
tid:1 name:iqn.2006-02.com.example.iserv:systems
        lun:0 state:0 iotype:fileio path:/dev/mapper/system-v3
        lun:1 state:0 iotype:fileio path:/dev/hda4
        lun:2 state:0 iotype:fileio path:/var/lib/xen/images/xen-1

There are many more options that control the behavior of the iSCSI target. Find them in the manual page of ietd.conf.

Active sessions are also displayed in the /proc file system. For each connected initiator, an extra entry is added to /proc/net/iet/session:

cat /proc/net/iet/session
tid:1 name:iqn.2006-02.com.example.iserv:system-v3
   sid:562949957419520 initiator:iqn.2005-11.de.suse:cn=rome.example.com,01.9ff842f5645
      cid:0 ip:192.168.178.42 state:active hd:none dd:none
   sid:281474980708864 initiator:iqn.2006-02.de.suse:01.6f7259c88b70
      cid:0 ip:192.168.178.72 state:active hd:none dd:none

When changes to the iSCSI target configuration are necessary, you always must restart the target to activate changes that are done in the configuration file. Unfortunately, all active sessions are interrupted in this process. To maintain an undisturbed operation, the changes should be done in the main configuration file /etc/ietd.conf, but also made manually to the current configuration with the administration utility ietadm.

To create a new iSCSI target with a LUN, first update your configuration file. The additional entry could be:

Target iqn.2006-02.com.example.iserv:system2
          Lun 0 Path=/dev/mapper/system-swap2
          IncomingUser joe secret

To set up this configuration manually, proceed as follows:

It is also possible to delete active connections. First, check all active connections with the command cat /proc/net/iet/session. This may look like:

cat /proc/net/iet/session
tid:1 name:iqn.2006-03.com.example.iserv:system
        sid:281474980708864 initiator:iqn.1996-04.com.example:01.82725735af5
                cid:0 ip:192.168.178.72 state:active hd:none dd:none

To delete the session with the session ID 281474980708864, use the command ietadm --op delete --tid=1 --sid=281474980708864 --cid=0. Be aware that this makes the device unaccessible on the client system and processes accessing this device are likely to hang.

ietadm can also be used to change various configuration parameters. Obtain a list of the global variables with ietadm --op show --tid=1 --sid=0. The output looks like:

InitialR2T=Yes
ImmediateData=Yes
MaxConnections=1
MaxRecvDataSegmentLength=8192
MaxXmitDataSegmentLength=8192
MaxBurstLength=262144
FirstBurstLength=65536
DefaultTime2Wait=2
DefaultTime2Retain=20
MaxOutstandingR2T=1
DataPDUInOrder=Yes
DataSequenceInOrder=Yes
ErrorRecoveryLevel=0
HeaderDigest=None
DataDigest=None
OFMarker=No
IFMarker=No
OFMarkInt=Reject
IFMarkInt=Reject

All of these parameters may be changed easily. For example, if you want to change the maximum number of connections to two, use ietadm --op update --tid=1 --params=MaxConnections=2. In the file /etc/ietd.conf, the associated line should look like MaxConnections 2.

	Update ietd.conf According to Changes with ietadm
The changes that you make with the command ietadm are not permanent for the system. These changes are lost at the next reboot if they are not added to the configuration file /etc/ietd.conf. Depending on the usage of iSCSI in your network, this may lead to severe problems.

There are several more options available for the command ietadm. Find an overview with ietadm -h. The abbreviations there are target ID (tid), session ID (sid), and connection ID (cid). They can also be found in /proc/net/iet/session.

The configuration is divided into three tabs. The Service tab may be used to enable the iSCSI initiator at boot time. It also offers to set a unique Initiator Name and an iSNS server to use for the discovery. The default port for iSNS is 3205. The Connected Targets tab gives an overview of the currently connected iSCSI targets. Like the Discovered Targets tab, it gives the option to add new targets to the system. Discovered Targets is the tab to start with. It provides the possibility of discovering iSCSI targets in the network.

After a successful discovery, use Login to activate the target. You will be asked for authentication information to use the selected iSCSI target. Next finishes the configuration. If everything went well, the target now appears in Connected Targets.

The virtual iSCSI device is now available. Find the actual device with lsscsi:

lsscsi
[1:0:0:0]   disk    IET      VIRTUAL-DISK     0     /dev/sda

Both the discovery and the configuration of iSCSI connections require a running iscsid. When running the discovery the first time, the internal database of the iSCSI initiator is created in the directory /var/lib/open-iscsi.

If your discovery is password protected, provide the authentication information to iscsid. Because the internal database does not exist when doing the first discovery, it cannot be used at this time. Instead, the configuration file /etc/iscsid.conf must be edited to provide the information. To add your password information for the discovery, add the following lines to the end of /etc/iscsid.conf:

discovery.sendtargets.auth.authmethod = CHAP
discovery.sendtargets.auth.username = <username>
discovery.sendtargets.auth.password = <password>

The discovery stores all received values in an internal persistent database. In addition, it displays all detected targets. Run this discovery with the command iscsiadm -m discovery --type=st --portal=<targetip>. The output should look like:

149.44.171.99:3260,1 iqn.2006-02.com.example.iserv:systems

To discover the available targets on a iSNS server, use the command iscsiadm --mode discovery --type isns --portal <targetip>

For each target defined on the iSCSI target, one line appears. Learn how to obtain more information about the stored data in Section 12.2.4, “The iSCSI Client Databases”.

The special --login option of iscsiadm creates all needed devices:

iscsiadm -m node -n iqn.2006-02.com.example.iserv:systems --login

The newly generated devices show up in the output of lsscsi and can now be accessed by mount.

LVM startup is supported by udev, so that any LVM volume groups will be activated automatically via udev once all required physical volumes have been detected.

LVM autoassembly in udev makes use of the udev helper program collect. This program takes as the first argument an abstract ID to be checked, followed by a list of component IDs. Once this program has been called with each of the component IDs as the first argument it'll return 0.

So for autoassembly the physical volume UUIDs for the given volume group is registered as argument list for collect. udev (or rather vol_id) is capable of detecting the physical volume UUID on a device and hence it can be passed as the first argument to collect.

Once collect has been called with all physical volume UUIDs (i.e. udev has received events for all component devices) the next rule triggers which just calls vgchange -a y <vgname> and the volume group will be activated.

All information that was discovered by the iSCSI initiator is stored in two database files that reside in /var/lib/open-iscsi. There is one database for the discovery of targets and one for the discovered nodes. When accessing a database, you first must select if you want to get your data from the discovery or from the node database. Do this with the -m discovery and -m node parameters of iscsiadm. Using iscsiadm just with one of these parameters gives an overview of the stored records:

iscsiadm -m discovery
149.44.171.99:3260,1 iqn.2006-02.com.example.iserv:systems

The target name in this example is iqn.2006-02.com.example.iserv:systems. This name is needed for all actions that relate to this special data set. To examine the content of the data record with the ID iqn.2006-02.com.example.iserv:systems, use the following command:

iscsiadm -m node --targetname iqn.2006-02.com.example.iserv:systems
node.name = iqn.2006-02.com.example.iserv:systems
node.transport_name = tcp
node.tpgt = 1
node.active_conn = 1
node.startup = manual
node.session.initial_cmdsn = 0
node.session.reopen_max = 32
node.session.auth.authmethod = CHAP
node.session.auth.username = joe
node.session.auth.password = ********
node.session.auth.username_in = <empty>
node.session.auth.password_in = <empty>
node.session.timeo.replacement_timeout = 0
node.session.err_timeo.abort_timeout = 10
node.session.err_timeo.reset_timeout = 30
node.session.iscsi.InitialR2T = No
node.session.iscsi.ImmediateData = Yes
....

To edit the value of one of these variables, use the command iscsiadm with the update operation. For example, if you want iscsid to log in to the iSCSI target when it initializes, set the variable node.startup to the value automatic:

iscsiadm -m node -n iqn.2006-02.com.example.iserv:systems --op=update --name=node.startup --value=automatic

Remove obsolete data sets with the operation delete. If the target iqn.2006-02.com.example.iserv:systems is no longer a valid record, delete this record with the command iscsiadm -m node -n iqn.2006-02.com.example.iserv:systems --op=delete. Use this option with caution because it deletes the record without any additional confirmation prompt.

To get a list of all discovered targets, run the command iscsiadm -m node.

The iSCSI protocol has been available for several years. There are many reviews and additional documentation comparing iSCSI with SAN solutions, doing performance benchmarks, or just describing hardware solutions. Important pages for more information about open-iscsi are:

There is also some online documentation available. See the manual pages of iscsiadm, iscsid, ietd.conf, and ietd and the example configuration file /etc/iscsid.conf.