Attaching an external storage system

Attach your external storage systems configurations through Fibre Channel or iSCSI connections with system nodes.

External storage systems attachment through Fibre Channel connections

All nodes in a system must be able to connect to the same set of ports on an external storage system. A system is considered degraded if it contains any two nodes that cannot connect to the same set of external storage-system ports. In such a situation, a system error is logged that requires a repair action.

Use one of the following techniques to control the access to the external storage systems:
  • Switch zoning
  • LUN-masking capability of the external storage systems

You can configure certain external storage systems to safely share resources between the system nodes and direct-attached hosts. This type of configuration is described as a split external storage system. In all cases, it is critical to configure the external storage system and SAN so that the system cannot access logical units (LUs) that a host or another system can also access. You can arrange the split external storage systems configuration by external storage-system logical unit number (LUN)-mapping and masking.

Configurations where an external storage system is split between two sets of system nodes are also supported. In all cases, it is critical to configure the external storage system and SAN so that the system nodes cannot access LUs that a host or another system can also access. You can use external storage systems LUN mapping and masking to arrange the configuration, failure to which can result in data corruption.

Attention: An external storage-system LU must not be shared between the system and a host or between more than one system. This configuration is not supported and is likely to cause undetected data loss or corruption. Ensure that only a single system can access each external storage-system LU

When an external storage system is detected on the Fibre Channel SAN, the system attempts to recognize it using its Inquiry data. If the device is not supported, the system configures the device as a generic device. A generic device might not function correctly when it is addressed by a node, especially under failure scenarios. However, the system does not regard accessing a generic device as an error condition and does not log an error. Managed disks (MDisks) that are presented by generic devices are not eligible to be used as quorum disks.

External storage systems attachment through iSCSI connections

Use the following guidelines to configure iSCSI-attached storage to the system:
  • Unlike Fibre Channel connections, manually configure the connections between the source system and the target external storage systems.
  • Discovery of the target IPs and session establishment is manually configured:
    • Either I/O group-wide - that is nodes from a specified I/O group discover and establish sessions, or
    • System-wide - that is all nodes discover and establish sessions.
  • After successful discovery, manually establish the initiator sessions from the source system to the target external storage system through:
    • Nodes in a specific I/O group, or
    • All nodes across the system.
  • A one-to-one mapping of source ports to target ports is required. The same numbered ports on each source system or node connect to only one port on each target system or node. Multiple initiator ports on the same system node cannot connect to the same target port (many-to-one connectivity). Similarly, one initiator port cannot be connected to multiple target ports on same target external storage system (one-to-many connectivity).
  • Zoning is not required.
  • Direct attachment between the system and external storage systems is not supported and requires Ethernet switches between the system and the external storage system.
  • To avoid a single point of failure, the guidelines suggest use of a dual-switch configuration. For full redundancy, a minimum of two paths between each initiator node and target node must be configured with each path going through a separate switch.
  • Extra paths can be configured to increase throughput if both initiator and target nodes support more ports.

External storage system direct attachment

If an external storage system with multiple World Wide Node Names (WWNN) is directly attached with the system, unexpected connectivity issues might occur for associated system controller objects in the system event log. Reason for the event logging is redundancy expectation of both initiator and target port connections between the system node and all the controller objects that are associated with the external storage system. In a direct attached configuration, the connection redundancy might not exist. To disable the unexpected event logs related to connection redundancy, use chcontroller -directattachenhanced yes command. For more information, see chcontroller command.