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Applies to SUSE Linux Enterprise Server 11 SP4 11 SP4

13 iSNS for Linux

Storage area networks (SANs) can contain many disk drives that are dispersed across complex networks. This can make device discovery and device ownership difficult. iSCSI initiators must be able to identify storage resources in the SAN and determine whether they have access to them.

Internet Storage Name Service (iSNS) is a standards-based service that facilitates the automated discovery, management, and configuration of iSCSI devices on a TCP/IP network. iSNS provides intelligent storage discovery and management services comparable to those found in Fibre Channel networks.

Important
Important

iSNS should be used only in secure internal networks.

13.1 How iSNS Works

For an iSCSI initiator to discover iSCSI targets, it needs to identify which devices in the network are storage resources and what IP addresses it needs to access them. A query to an iSNS server returns a list of iSCSI targets and the IP addresses that the initiator has permission to access.

Using iSNS, you create iSNS discovery domains and discovery domain sets. You then group or organize iSCSI targets and initiators into discovery domains and group the discovery domains into discovery domain sets. By dividing storage nodes into domains, you can limit the discovery process of each host to the most appropriate subset of targets registered with iSNS, which allows the storage network to scale by reducing the number of unnecessary discoveries and by limiting the amount of time each host spends establishing discovery relationships. This lets you control and simplify the number of targets and initiators that must be discovered.

iSNS Discovery Domains and Discovery Domain Sets
Figure 13.1: iSNS Discovery Domains and Discovery Domain Sets

Both iSCSI targets and iSCSI initiators use iSNS clients to initiate transactions with iSNS servers by using the iSNS protocol. They then register device attribute information in a common discovery domain, download information about other registered clients, and receive asynchronous notification of events that occur in their discovery domain.

iSNS servers respond to iSNS protocol queries and requests made by iSNS clients using the iSNS protocol. iSNS servers initiate iSNS protocol state change notifications and store properly authenticated information submitted by a registration request in an iSNS database.

Some of the benefits provided by iSNS for Linux include:

  • Provides an information facility for registration, discovery, and management of networked storage assets.

  • Integrates with the DNS infrastructure.

  • Consolidates registration, discovery, and management of iSCSI storage.

  • Simplifies storage management implementations.

  • Improves scalability compared to other discovery methods.

An example of the benefits iSNS provides can be better understood through the following scenario:

Suppose you have a company that has 100 iSCSI initiators and 100 iSCSI targets. Depending on your configuration, all iSCSI initiators could potentially try to discover and connect to any of the 100 iSCSI targets. This could create discovery and connection difficulties. By grouping initiators and targets into discovery domains, you can prevent iSCSI initiators in one department from discovering the iSCSI targets in another department. The result is that the iSCSI initiators in a specific department only discover those iSCSI targets that are part of the department’s discovery domain.

13.2 Installing iSNS Server for Linux

iSNS Server for Linux is included with SLES 10 SP2 and later, but is not installed or configured by default. You must install the iSNS package modules (isns and yast2-isns modules) and configure the iSNS service.

Note
Note

iSNS can be installed on the same server where iSCSI target or iSCSI initiator software is installed. Installing both the iSCSI target software and iSCSI initiator software on the same server is not supported.

To install iSNS for Linux:

  1. Start YaST and select Network ServicesiSNS Server.

  2. When prompted to install the isns package, click Install.

  3. Follow the install instructions to provide the SUSE Linux Enterprise Server 11 installation disks.

    When the installation is complete, the iSNS Service configuration dialog box opens automatically to the Service tab.

  4. In Address of iSNS Server, specify the DNS name or IP address of the iSNS Server.

  5. In Service Start, select one of the following:

    • When Booting:  The iSNS service starts automatically on server startup.

    • Manually (Default):  The iSNS service must be started manually by entering rcisns start or /etc/init.d/isns start at the server console of the server where you install it.

  6. Specify the following firewall settings:

    • Open Port in Firewall:  Select the check box to open the firewall and allow access to the service from remote computers. The firewall port is closed by default.

    • Firewall Details:  If you open the firewall port, the port is open on all network interfaces by default. Click Firewall Details to select interfaces on which to open the port, select the network interfaces to use, then click OK.

  7. Click Finish to apply the configuration settings and complete the installation.

  8. Continue with Section 13.3, “Configuring iSNS Discovery Domains”.

13.3 Configuring iSNS Discovery Domains

In order for iSCSI initiators and targets to use the iSNS service, they must belong to a discovery domain.

Important
Important

The SNS service must be installed and running to configure iSNS discovery domains. For information, see Section 13.4, “Starting iSNS”.

13.3.1 Creating iSNS Discovery Domains

A default discovery domain named default DD is automatically created when you install the iSNS service. The existing iSCSI targets and initiators that have been configured to use iSNS are automatically added to the default discovery domain.

To create a new discovery domain:

  1. Start YaST and under Network Services, select iSNS Server.

  2. Click the Discovery Domains tab.

    The Discovery Domains area lists all discovery domains. You can create new discovery domains, or delete existing ones.Deleting a domain removes the members from the domain, but it does not delete the iSCSI node members.

    The Discovery Domain Members area lists all iSCSI nodes assigned to a selected discovery domain. Selecting a different discovery domain refreshes the list with members from that discovery domain. You can add and delete iSCSI nodes from a selected discovery domain. Deleting an iSCSI node removes it from the domain, but it does not delete the iSCSI node.

    Creating an iSCSI node allows a node that is not yet registered to be added as a member of the discovery domain. When the iSCSI initiator or target registers this node, then it becomes part of this domain.

    When an iSCSI initiator performs a discovery request, the iSNS service returns all iSCSI node targets that are members of the same discovery domain.

  3. Click the Create Discovery Domain button.

    You can also select an existing discovery domain and click the Delete button to remove that discovery domain.

  4. Specify the name of the discovery domain you are creating, then click OK.

  5. Continue with Section 13.3.2, “Creating iSNS Discovery Domain Sets”.

13.3.2 Creating iSNS Discovery Domain Sets

Discovery domains must belong to a discovery domain set. You can create a discovery domain and add nodes to that discovery domain, but it is not active and the iSNS service does not function unless you add the discovery domain to a discovery domain set. A default discovery domain set named default DDS is automatically created when you install iSNS and the default discovery domain is automatically added to that domain set.

To create a discovery domain set:

  1. Start YaST and under Network Services, select iSNS Server.

  2. Click the Discovery Domains Sets tab.

    The Discovery Domain Sets area lists all of the discover domain sets. A discovery domain must be a member of a discovery domain set in order to be active.

    In an iSNS database, a discovery domain set contains discovery domains, which in turn contains iSCSI node members.

    The Discovery Domain Set Members area lists all discovery domains that are assigned to a selected discovery domain set. Selecting a different discovery domain set refreshes the list with members from that discovery domain set. You can add and delete discovery domains from a selected discovery domain set. Removing a discovery domain removes it from the domain set, but it does not delete the discovery domain.

    Adding an discovery domain to a set allows a not yet registered iSNS discovery domain to be added as a member of the discovery domain set.

  3. Click the Create Discovery Domain Set button.

    You can also select an existing discovery domain set and click the Delete button to remove that discovery domain set.

  4. Specify the name of the discovery domain set you are creating, then click OK.

  5. Continue with Section 13.3.3, “Adding iSCSI Nodes to a Discovery Domain”.

13.3.3 Adding iSCSI Nodes to a Discovery Domain

  1. Start YaST and under Network Services, select iSNS Server.

  2. Click the iSCSI Nodes tab.

  3. Review the list of nodes to ensure that the iSCSI targets and initiators that you want to use the iSNS service are listed.

    If an iSCSI target or initiator is not listed, you might need to restart the iSCSI service on the node. You can do this by running the rcopen-iscsi restart command to restart an initiator or the rciscsitarget restart command to restart a target.

    You can select an iSCSI node and click the Delete button to remove that node from the iSNS database. This is useful if you are no longer using an iSCSI node or have renamed it.

    The iSCSI node is automatically added to the list (iSNS database) again when you restart the iSCSI service or reboot the server unless you remove or comment out the iSNS portion of the iSCSI configuration file.

  4. Click the Discovery Domains tab, select the desired discovery domain, then click the Display Members button.

  5. Click Add existing iSCSI Node, select the node you want to add to the domain, then click Add Node.

  6. Repeat Step 5 for as many nodes as you want to add to the discovery domain, then click Done when you are finished adding nodes.

    An iSCSI node can belong to more than one discovery domain.

  7. Continue with Section 13.3.4, “Adding Discovery Domains to a Discovery Domain Set”.

13.3.4 Adding Discovery Domains to a Discovery Domain Set

  1. Start YaST and under Network Services, select iSNS Server.

  2. Click the Discovery Domains Set tab.

  3. Select Create Discovery Domain Set to add a new set to the list of discovery domain sets.

  4. Choose a discovery domain set to modify.

  5. Click Add Discovery Domain, select the discovery domain you want to add to the discovery domain set, then click Add Discovery Domain.

  6. Repeat the last step for as many discovery domains as you want to add to the discovery domain set, then click Done.

    A discovery domain can belong to more than one discovery domain set.

13.4 Starting iSNS

iSNS must be started at the server where you install it. Enter one of the following commands at a terminal console as the root user:

rcisns start
/etc/init.d/isns start

You can also use the stop, status, and restart options with iSNS.

iSNS can also be configured to start automatically each time the server is rebooted:

  1. Start YaST and under Network Services, select iSNS Server.

  2. With the Service tab selected, specify the IP address of your iSNS server, then click Save Address.

  3. In the Service Start section of the screen, select When Booting.

    You can also choose to start the iSNS server manually. You must then use the rcisns start command to start the service each time the server is restarted.

13.5 Stopping iSNS

iSNS must be stopped at the server where it is running. Enter one of the following commands at a terminal console as the root user:

rcisns stop
/etc/init.d/isns stop

13.6 For More Information

For information, see the Linux iSNS for iSCSI project. The electronic mailing list for this project is Linux iSNS - Discussion.

General information about iSNS is available in RFC 4171: Internet Storage Name Service.