20 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
2.5.1  Hosts
A host system is a server that is connected to IBM Storwize V7000 through a Fibre Channel 
connection, Fibre Channel over Ethernet (FCoE), or through an internet SCSI (iSCSI) 
connection.
Hosts are defined to IBM Spectrum Virtualize by identifying their worldwide port names 
(WWPNs) for Fibre Channel hosts. For iSCSI hosts, they are identified by using their iSCSI 
names. The iSCSI names can be iSCSI qualified names (IQNs) or extended unique identifiers 
(EUIs).
2.5.2  Host cluster
Host cluster is a host object in the IBM Storwize V7000. A host cluster is a combination of two 
or more servers that is connected to IBM Storwize V7000 through a Fibre Channel, FCoE, or 
iSCSI connection. Host cluster object can see the same set of volumes.
2.5.3  Nodes or canisters
An IBM Storwize V7000 can have 2 - 8 hardware components, called nodes, node canisters, 
or canisters. They perform the virtualization of internal and external volumes and the cache 
and copy services (remote copy) functions. A clustered system consists of 1 - 4 node pairs.
One of the canisters within the system is known as the configuration node. This node 
manages configuration activity for the clustered system. If this node fails, the system 
automatically nominates another node to become the configuration node.
Because the active nodes are installed in pairs, each node provides a failover function to its 
partner node if a node fails.
2.5.4  I/O groups
Within IBM Storwize V7000, 1 - 4 pairs of node canisters are known as I/O groups. The IBM 
Storwize V7000 with installed IBM Spectrum Virtualize supports eight node canisters in the 
clustered system, which provides four I/O groups. 
When a host server performs I/O to one of its volumes, all the I/Os for a specific volume are 
directed to the I/O group. Also, under normal conditions, the I/Os for that specific volume are 
always processed by the same node within the I/O group.
One node of the I/O group acts as a preferred node for its own specific subset of the total 
number of volumes that the I/O group presents to the host servers (a maximum of 2048 
volumes per I/O group). However, each node also acts as a failover node for its partner node 
within the I/O group, so a node takes over the I/O workload from its partner node, if required, 
with no effect to the server’s application.
In an IBM Storwize V7000 environment, the use of active/active architecture and the I/O 
handling for a volume can be managed by both nodes of the I/O group. Therefore, servers 
that are connected through Fibre Channel connectors must use multipath device drivers 
handle this capability.
The IBM Storwize V7000 I/O groups are connected to the SAN so that all application servers 
accessing volumes from the I/O group have access to them. Up to 2048 host server objects 
can be defined in four I/O groups.