IBM Midrange System DS4000 Series Hardware Manual page 135

Storage partition topology is a collection of topological elements (default group, host groups,
hosts, and host ports) shown as nodes in the topology view of the Mappings View. To map a
logical drive or LUN to a specific host server or group of hosts, each component of the
storage partition must be defined.
A storage partition contains several components:
Host groups
Hosts
Host ports
Logical drive mappings
host group
A is a collection of hosts that are allowed to access certain logical drives, for
example, a cluster of two systems.
host
A is a single system that can be mapped to a
host port
A is the identifier of a port on a Fibre Channel host bus adapter (HBA), identified by
its world-wide name (WWN), or the identifier of the initiator name running the iSCSI protocol.
A single host can contain more than one host port. If the servers are attached in a redundant
way (highly recommended), each server will have two host bus adapters, that is, it needs two
host ports within the same host system. It is possible to have a host with a single HBA, but for
redundancy, it should be able to access both DS5000 controllers. When using FC, this
redundancy can be achieved using SAN zoning, and when using iSCSI, it is provided by the
Ethernet switch.
The DS5000 storage subsystem only communicates through the use of this host port's
identifiers. The storage system is not aware of which host bus adapters are in the same
server or in servers that have a certain relationship, such as a cluster. The host groups, the
hosts, and their host ports reflect a logical view of the physical connections to the storage, as
well as the logical connection between servers, such as clusters.
With the logical setup defined previously, mappings are specific assignments of logical drives
to particular host groups or hosts.
The storage partition is the combination of all these components. It ensures proper access to
the different logical drives even if there are several hosts or clusters connected.
The default host group is a placeholder for hosts that are defined but have not been mapped.
The default host group is also normally used only when storage partitioning is not enabled. If
this is the case, then only one type of operating system should be sharing the logical drives.
Every unassigned logical drive is mapped to the undefined mappings group. This means no
host (or host port, to be precise) can access these logical drives until they are mapped.
With Storage Manager, it is possible to have up to 512 storage partitions on a DS5000. This
allows the storage subsystem to have storage capacity to a greater amount of heterogeneous
hosts, allowing for greater flexibility and scalability.
logical drive
Chapter 4. IBM System Storage DS planning and configuration
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