Configuring an enhanced stretched system

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An enhanced stretched system assists with site disaster recovery. An enhanced stretched topology system can be configured through site allocation and topology change command-line (CLI) commands. The management GUI can also be used to configure a stretched topology with the Modify System Topology wizard. If you are using iSCSI-attached external storage in the stretched system configuration, you also need to add the storage to the system and specify the site for the iSCSI-attached storage system.

Before you begin

If you are using RDMA-capable Ethernet ports to connect nodes in a stretched system, you must ensure all prerequisites are complete and define all RDMA-capable Ethernet ports before configuring the stretched system. For information, see the topics on Configuration details for using RDMA-capable Ethernet ports to connect nodes and Configuring a system with RDMA-capable Ethernet ports.

About this task

You can use either the management GUI or the command-line interface to configure an enhanced stretched system. The management GUI supports a wizard that completes all the steps to create an enhanced stretched system, including site definitions for nodes, hosts, and external storage systems. The CLI process requires that each of these steps are completed separately.

Using the management GUI

Select Monitoring > System.
In the System Actions menu, select Modify System Topology. Use the wizard to complete the configuration.

Using the command line interface

To configure your clustered system site information in the command-line interface, complete these steps.

Procedure

Use the following commands addnode or chnode and chcontroller and chhost to assign site information to the nodes, hosts and external storage systems in site 1, 2, and 3.
Note: Site 3 cannot be assigned to any node and contains only external storage systems that are used for quorum.
For example, enter the following command to change site definitions for a node:
```
chnode -site site_id node node_id
```
where site_id is the identifier for the site and node_id is the identifier of the node.
Enter the following command to see the node configuration details for site 1 on node 1:
```
lsnode 1
```
Enter the following command to assign site information to all the external storage systems by using the following command:
```
chcontroller –site site_id controller_id
```
where
To view the site for the external storage system for and MDisk information, enter the following commands:
```
lscontroller controller_id
lsmdisk object_id
```
Issue this command to change to site 1 on host 1:
```
chost -site 1 host_name
```
Issue this command to see the node configuration details for site 1 on node 1:
```
lshost host_name
```
When site awareness is provided to the entities that are wanted in all the three sites, change the system topology to stretched.
In the CLI, enter the following command:
```
chsystem -topology stretched
```
You can use the lssystem command to verify that the topology is stretched.
```
 lssystem 
```
Note: The quorum disk assignment changes automatically after the system topology is stretched. The active quorum disk is at site 3. Sites 1 and 2 each have one inactive quorum disk.

Configuring an external iSCSI storage system

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About this task

After you configure the stretched system and all nodes and hosts are assigned to sites, you can add any iSCSI-attached storage and assign it a specific site in the stretched system. The Modify System Topology wizard automatically detects any Fibre Channel-attached storage but iSCSI storage must be added manually before the site assignments can be configured. You can use either the management GUI or the command-line interface to add supported iSCSI attached storage to the stretched system.

Using the Management GUI

After you configure the stretched topology, add the iSCSI attached storage by completing the following steps:

If you are using iSCSI-attached external storage, you must add the storage to the system and specify the site by using the Add iSCSI External Storage wizard. To access the wizard, select Pools > External Storage > Add iSCSI External Storage.
Select the type of storage system that you are adding. The system supports iSCSI connections to Storwize family products and to Dell Equallogic that are used as external storage.
Enter the information for the source and target ports for the iSCSI connection and specify the site for the iSCSI-attached storage.

Using the command-line interface

After you change the system topology to stretched and nodes are assigned sites, complete these steps to add iSCSI attached storage systems to the configuration. If you are using the command-line interface to add iSCSI storage, complete these steps:

From the nodes of site 1, discover the iSCSI target storage system:
```
detectiscsistorageportcandidate –srcportid 1
 -targetip IP1 -site 1 
```

Check the status of the discovered targets:

lsiscsistorageportcandidate id src_port_id target_ipv4 | target_ipv6
 target_iscsiname iogroup_list configured status
 site_id site_name 0 1 IP1 IQN1 1:1:1:1 no Full 1 site1

From the nodes of site 1, add a session to the discovered targets:
```
addiscsitorageport -site 1 0
```

From the nodes of site 1, view the established sessions with the target:

id src_port_id target_ipv4 | target_ipv6 target_iscsiname
 controller_id iogroup_list status site_id site_name
 0 3 IP1 IQN1 5 1:1:1:1 full 1 site1

The new storage system can be shown as available by entering the lscontroller command. Assign a site:
```
chcontroller -site 1 controllerID
```
From the system nodes of site 2, repeat steps 1 through 5 for discovering and establishing sessions to the same iSCSI controller or a different iSCSI controller.