External storage system configuration details (Fibre Channel)
Plan for your external storage system configurations through Fibre Channel connections with a node.
See the following website for the latest support information:
All nodes in a system must be able to connect to the same set of storage system ports on each device. A system that contains any two nodes that cannot connect to the same set of storage-system ports is considered degraded. In this situation, a system error is logged that requires a repair action. This rule can have important effects on a storage system which has exclusion rules that determine to which host bus adapter (HBA) worldwide node names (WWNNs) a storage partition can be mapped.
A storage-system logical unit (LU) must not be shared between the system and a host.
You can configure certain storage systems to safely share resources between the node and direct-attached hosts. This type of configuration is described as a split storage system. In all cases, it is critical that you configure the storage system and SAN so that the system cannot access logical units (LUs) that a host or another system can also access. This split storage system configuration can be arranged by storage system logical unit number (LUN) mapping and masking. If the split storage system configuration is not guaranteed, data corruption can occur.
Configurations where a storage system is split between two nodes are also supported. In all cases, it is critical that you configure the storage system and SAN so that the node cannot access LUs that a host or another node can also access. You can use storage system LUN mapping and masking to arrange for this configuration. If this configuration is not guaranteed, data corruption can occur.
Unsupported storage systems
When a storage system is detected on the 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.
Split storage-system configuration details
The system is configured to manage LUs that are exported only by RAID storage systems. Non-RAID storage systems are not supported. If you are using the node to manage flash drive or other JBOD (just a bunch of disks) LUs that are presented by non-RAID storage systems, the system itself does not provide RAID functions. These LUs are exposed to data loss when a disk failure occurs.
If a single RAID storage system presents multiple LUs, either by having multiple RAIDs configured or by partitioning one or more RAID into multiple LUs, each LU can be owned by either the system or a direct-attached host. LUN masking must also be configured to ensure that LUs are not shared between the nodes and direct-attach hosts.
In a split storage-system configuration, a storage system presents some of its LUs to a node (which treats the LU as an MDisk) and the remaining LUs to another host. The node presents volumes that are created from the MDisk to another host. There is no requirement for the multi-pathing driver for the two hosts to be the same. Figure 1 shows that the RAID storage system could be an IBM® DS4000®, for example, with RDAC used for pathing on the directly attached host, and SDD used on the host that is attached with the node. Hosts can simultaneously access LUs that are provided by the system and directly by the device.
