You must follow the configuration rules for SAN Volume Controller nodes to ensure that you have a valid configuration.
SAN Volume Controller 2145-4F2 and SAN Volume Controller 2145-8F2 nodes contain two 2-port host bus adapters (HBAs). If one HBA fails, the node operates in degraded mode. If an HBA is physically removed, the configuration is not supported.
SAN Volume Controller 2145-CF8, SAN Volume Controller 2145-8F4, SAN Volume Controller 2145-8G4, and SAN Volume Controller 2145-8A4 nodes contain one 4-port HBA.
Each node presents a virtual disk (VDisk) to the SAN through four ports. Each VDisk is accessible from the two nodes in an I/O group. Each HBA port can recognize up to eight paths to each logical unit (LU) that is presented by the cluster. The hosts must run a multipathing device driver before the multiple paths can resolve to a single device. You can use fabric zoning to reduce the number of paths to a VDisk that are visible by the host.
The number of paths through the network from an I/O group to a host must not exceed eight; configurations that exceed eight paths are not supported. Each node has four ports and each I/O group has two nodes. Therefore, without any zoning, the number of paths to a VDisk is eight multiplied by the number of host ports.
Clusters that use the intercluster Metro Mirror and Global Mirror feature can use optical fiber connections between the switches, or they can use distance-extender technology that is supported by the switch manufacturer.
To ensure cluster failover operations, Ethernet port 1 on all nodes must be connected to the same set of subnets. If used, Ethernet port 2 on all nodes must also be connected to the same set of subnets. However, the subnets for Ethernet port 1 do not have to be the same as Ethernet port 2.
The physical distance between SAN Volume Controller nodes in the same cluster is limited to 100 meters due to connectivity requirements and servicing requirements. Several of the SAN Volume Controller service actions in problem situations require that the manipulations be done to both SAN Volume Controller nodes within an I/O group or a cluster within one minute of each other. Set up your cluster environment to enable IBM® service personnel to easily perform actions that are almost simultaneous in the required timeframe.
A SAN Volume Controller node must be in the same rack as the uninterruptible power supply from which it is supplied.
The depth of the SAN Volume Controller 2145-8A4 node is less than other components or nodes by approximately 127 mm or 5 inches. SAN Volume Controller 2145-8A4 nodes should not be located in the rack between components or nodes with greater depths; otherwise, it will not be possible to attach cables to a SAN Volume Controller 2145-8A4 node.
SAN Volume Controller supports shortwave and longwave fibre-channel connections between SAN Volume Controller nodes and the switches that they are connected to.
To avoid communication between nodes that are being routed across interswitch links (ISLs), connect all SAN Volume Controller nodes to the same fibre-channel switches.
No ISL hops are permitted among the SAN Volume Controller nodes within the same I/O group. However, one ISL hop is permitted among SAN Volume Controller nodes that are in the same cluster though different I/O groups. If your configuration requires more than one ISL hop for SAN Volume Controller nodes that are in the same cluster but in different I/O groups, contact your IBM service representative.
To avoid communication between nodes and storage systems that are being routed across ISLs, connect all storage systems to the same fibre-channel switches as the SAN Volume Controller nodes. One ISL hop between the SAN Volume Controller nodes and the storage controllers is permitted. If your configuration requires more than one ISL, contact your IBM service representative.
In larger configurations, it is common to have ISLs between host systems and the SAN Volume Controller nodes.
The fibre-channel ports on SAN Volume Controller 2145-CF8 nodes can operate at 2 Gbps, 4 Gbps, or 8 Gbps. The fibre-channel ports on SAN Volume Controller 2145-8F4, SAN Volume Controller 2145-8G4 and SAN Volume Controller 2145-8A4 nodes can operate at 1 Gbps, 2 Gbps, or 4 Gbps. The fibre-channel ports on all these node types autonegotiate the link speed that is used with the FC switch. The ports normally operate at the maximum speed that is supported by both the SAN Volume Controller port and the switch. However, if a large number of link errors occur, the ports might operate at a lower speed than what could be supported.
Fibre-channel ports on SAN Volume Controller 2145-4F2 and SAN Volume Controller 2145-8F2 nodes cannot autonegotiate the speed at which they operate. You must set the required speed manually; the optical fiber connections between the fibre-channel switches and all SAN Volume Controller 2145-4F2 and SAN Volume Controller 2145-8F2 nodes in a cluster must run at the same speed.