Apply the following Lenovo Storage V series configuration details for Fibre Channel switches to ensure that you have a valid configuration.
SAN fabric function is available only if a Fibre Channel option is installed. Otherwise, this information does not apply.
Configuring your SAN with at least two independent switches, or networks of switches, ensures a redundant fabric with no single point of failure. If one of the two SAN fabrics fails, the configuration is in a degraded mode, but is still valid. Maintain separate fabrics for FCoE and FC. If you attempt to combine these fabrics, you might risk adding more paths to the volumes. Supported configurations allow a maximum of eight paths. A SAN with only one fabric is a valid configuration but risks loss of access to data if the fabric fails. SANs with only one fabric are exposed to a single point of failure.
For Fibre Channel connections, the Lenovo Storage V series node canisters must be connected to either SAN switches or directly connected to a host port. If the Lenovo Storage V series system contains more than one control enclosure, a minimum of two Fibre Channel ports from each node canister must be connected to the SAN to provide connections to each of the counterpart SANs that are in the redundant fabric. When iSCSI hosts are attached to Lenovo Storage V series node canisters, Ethernet switches must be used.
All back-end storage systems must always be connected to SAN switches only. Multiple connections are permitted from redundant storage systems to improve data bandwidth performance. A connection between each redundant storage system and each counterpart SAN is not required. For example, in an IBMDS4000 configuration in which the IBM® DS4000™ contains two redundant storage systems, only two storage system minihubs are usually used. Storage system A is connected to counterpart SAN A, and storage system B is connected to counterpart SAN B. Any configuration that uses a direct physical connection between the Lenovo Storage V series node and the storage system is not supported.
When you attach a node to a SAN fabric that contains core directors and edge switches, connect the node ports to the core directors and connect the host ports to the edge switches. In this type of fabric, the next priority for connection to the core directors is the storage systems, leaving the host ports connected to the edge switches.
A Lenovo Storage V series SAN must follow all switch manufacturer configuration rules, which might place restrictions on the configuration. Any configuration that does not follow switch manufacturer configuration rules is not supported.
Mixing manufacturer switches in a single SAN fabric
Within an individual SAN fabric, only mix switches from different vendors if the configuration is supported by the switch vendors. When you use this option for FCF Switch to FC Switch connectivity, review and plan as documented in ISL oversubscription.
Fibre Channel switches and interswitch links
Lenovo Storage V series supports distance-extender technology, including dense wavelength division multiplexing (DWDM) and Fibre Channel over IP (FCIP) extenders, to increase the overall distance between local and remote clustered systems (systems). If this extender technology involves a protocol conversion, the local and remote fabrics are regarded as independent fabrics, limited to three ISL hops each.
With ISLs between nodes in the same system, the inter-switch links (ISLs) are considered a single point of failure. Figure 1 illustrates this example.
If Link 1 or Link 2 fails, the system communication does not fail.
If Link 3 or Link 4 fails, the system communication does not fail.
If ISL 1 or ISL 2 fails, the communication between Node A and Node B fails for a period of time, and the node is not recognized, even though there is still a connection between the nodes.
To ensure that a Fibre Channel link failure does not cause nodes to fail when there are ISLs between nodes, it is necessary to use a redundant configuration. This configuration is illustrated in Figure 2.
With a redundant configuration, if any one of the links fails, communication on the system does not fail.
ISL oversubscription
Perform a thorough SAN design analysis to avoid ISL congestion. Do not configure the SAN to use Lenovo Storage V series to Lenovo Storage V series traffic or Lenovo Storage V series to storage system traffic across ISLs that are oversubscribed. For host to Lenovo Storage V series traffic, do not use an ISL oversubscription ratio that is greater than 7 to 1. Congestion on the ISLs can result in severe Lenovo Storage V series performance degradation and I/O errors on the host.
ISL oversubscription rules apply to FCoE Switches.
Lenovo Storage V series in a SAN with director class switches
You can use director class switches within the SAN to connect large numbers of RAID controllers and hosts to a Lenovo Storage V series system. Because director class switches provide internal redundancy, one director class switch can replace a SAN that uses multiple switches. However, the director class switch provides only network redundancy; it does not protect against physical damage (for example, flood or fire), which might destroy the entire function. A tiered network of smaller switches or a core-edge topology with multiple switches in the core can provide comprehensive redundancy and more protection against physical damage for a network in a wide area. Do not use a single director class switch to provide more than one counterpart SAN because this configuration does not constitute true redundancy.