Ensure that you understand the basic terms and definitions when you are configuring the SAN Volume Controller within the SAN fabric or a local area network (LAN).
Table 1 provides terms and definitions that can guide your understanding of the SAN fabric rules and requirements.
| Term | Definition |
|---|---|
| ISL hop | A hop on an interswitch link (ISL). With reference to all pairs of N-ports or end-nodes that are in a fabric, the number of ISL hops is the number of links that are crossed on the shortest route between the node pair whose nodes are farthest apart from each other. The distance is measured only in terms of the ISL links that are in the fabric. |
| Oversubscription | The ratio of the sum of the traffic that is
on the initiator N-node connections to the traffic that is on the
most heavily loaded ISLs or where more than one ISL is in parallel
between these switches. This definition assumes that there is a symmetrical network and a specific
workload that is applied equally from all initiators and sent equally
to all targets. A symmetrical network is one in which
all initiators are connected at the same level and all the controllers
are connected at the same level. Note: The SAN Volume Controller puts
its back-end traffic onto the same symmetrical network. The back-end
traffic can vary by workload. Therefore, the oversubscription that
a 100% read hit gives is different from the oversubscription that
100% write-miss gives. If you have an oversubscription of 1 or less,
the network is nonblocking.
|
| Virtual SAN (VSAN) | A virtual storage area network (SAN). |
| Redundant SAN | A SAN configuration in which if any one component fails, connectivity between the devices that are in the SAN is maintained, possibly with degraded performance. You can create a redundant SAN by splitting the SAN into two independent counterpart SANs. |
| Counterpart SAN | A nonredundant portion of a redundant SAN. A counterpart SAN provides all the connectivity of the redundant SAN, but without the redundancy. The SAN Volume Controller is typically connected to a redundant SAN that is made out of two counterpart SANs. |
| Local fabric | The fabric that consists of those SAN components (switches and cables) that connect the components (nodes, hosts, and switches) of the local cluster. Because the SAN Volume Controller supports Metro Mirror and Global Mirror, significant distances might exist between the components of the local cluster and those of the remote clusters. |
| Remote fabric | The fabric that consists of those SAN components (switches and cables) that connect the components (nodes, hosts, and switches) of the remote cluster. Because the SAN Volume Controller supports Metro Mirror and Global Mirror, significant distances might exist between the components of the local cluster and those of the remote clusters. |
| Local/remote fabric interconnect | The SAN components that connect the local fabrics to the remote fabrics. There might be significant distances between the components in the local cluster and those in the remote cluster. These components might be single-mode optical fibers that are driven by gigabit interface converters (GBICs), or they might be other, more advanced components, such as channel extenders. |
| SAN Volume Controller fibre-channel port fan in | The number of hosts that can see any one port. Some controllers recommend that the number of hosts using each port be limited to prevent excessive queuing at that port. If the port fails or the path to that port fails, the host might fail over to another port, and the fan in requirements might be exceeded in this degraded mode. |
| Not valid configuration | The current SAN configuration is not correct. An attempted operation failed and generated an error code that indicates what caused it to become "not valid." The most likely cause is that either a device has failed, or a device has been added to the SAN that has caused the configuration to be marked as not valid. |
| Unsupported configuration | A configuration that could operate successfully, but that IBM® does not guarantee any solutions for if problems occur. Typically, this type of configuration does not create any error log entries. |
| Valid configuration | A configuration that consists
of devices and connections that are identified as valid and supported. Neither
of the following two conditions exist with the current configuration:
|
| Degraded | A valid configuration that has had a failure, but continues to be valid and supported. Typically, a repair action is required to restore the degraded configuration to a valid configuration. |
| Fibre-channel extender | A device for long distance communication that connects other SAN fabric components. Generally these components might involve protocol conversion to ATM, IP, or some other long-distance communication protocol. |
| Mesh configuration | A network that contains a number of small SAN switches that are configured to create a larger switched network. With this configuration, four or more switches are connected in a loop with additional direct connections between nonadjacent switches within the loop. An example of this configuration is four switches that are connected in a loop with ISLs for one of the diagonals. |
If you plan to use iSCSI to configure a LAN, ensure that you also understand the iSCSI terms and definitions. Table 2 highlights the terms and definitions for iSCSI.
| Term | Definition |
|---|---|
| Challenge Handshake Authentication Protocol (CHAP) | An authentication protocol that protects against eavesdropping by encrypting the user name and password. |
| Clustered Ethernet port | A physical Ethernet port on a node in a cluster that contains configuration settings that are shared by all the ports in a cluster. |
| Extended-unique identifier (EUI) | A unique iSCSI name that identifies an iSCSI target adapter or an iSCSI initiator adapter as defined by the iSCSI standard (RFC 3722). |
| Host object | A logical object that represents a list of worldwide port names (WWPNs) and a list of iSCSI names that identify the interfaces that the host system uses to communicate with a device. iSCSI names can be either iSCSI qualified names (IQNs) or extended-unique identifiers (EUIs). |
| Host system | A computer that is connected to the SAN Volume Controller through either a fibre-channel interface or an IP network. |
| Initiator | The system component that originates an I/O command over an I/O bus or network. I/O adapters and network interface controllers are typical initiators. |
| Internet Storage Name Service (iSNS) Protocol | A protocol that is used by a host system to manage iSCSI targets and iSCSI discovery. iSCSI initiators use the ISNS Protocol to locate the appropriate storage resources. |
| iSCSI alias | An alternative name for the iSCSI-attached host. |
| iSCSI name | A name that identifies an iSCSI target adapter or an iSCSI initiator adapter. An iSCSI name can be an iSCSI qualified name (IQN) or an extended-unique identifier (EUI). Typically, this identifier has the following format: iqn.datecode.reverse domain. |
| iSCSI qualified name (IQN) | A specific type of iSCSI name that identifies an iSCSI target adapter or an iSCSI initiator adapter as defined by the iSCSI standard (RFC 3722). |
| Network interface controller (NIC) | Hardware that provides the interface control between system main storage and external high-speed link (HSL) ports. |
| Node Ethernet port | A port that represents an iSCSI port on a SAN Volume Controller node. Configuration settings are specific to a single physical Ethernet port. |
| Subnet | A portion of a network that is divided into smaller independent subgroups, which still are interconnected. |
| Target | The program or system to which a request for files or processing is sent. |