7914DS3KPlanning_090710.fm Draft Document for Review March 28, 2011 12:24 pm
64 IBM System Storage DS3500: Introduction and Implementation Guide
needs. It enables you to connect multiple and heterogeneous host systems to the same
storage server, either in stand-alone or clustered mode. The term storage partitioning is
somewhat misleading, because it actually represents a host or a group of hosts and the
logical drives they access.
Without storage partitioning, the logical drives configured on a DS3500 Storage System can
only be accessed by a single host system or by a single cluster, which can lead to inefficient
use of storage server hardware unless the use of the DS3500 Storage System is dedicated to
a single host (for example, SVC attachment, where it is seen as a single host).
Storage partitioning, on the other hand, allows the creation of “sets”, containing the hosts with
their host bus adapters and the logical drives. We call these sets
storage partitions. The host
systems can only access their assigned logical drives, just as though these logical drives
were locally attached to them. Storage partitioning adapts the SAN idea of globally accessible
storage to the local-storage-minded operating systems.
Storage partitioning allows mapping and masks the logical drive or LUN (that is why it is also
referred to as “LUN masking”), which means that after the logical drive is assigned to a host,
it is hidden from all other hosts connected to the same storage server. Therefore, access to
that logical drive is exclusively reserved for that host.
It is a good practice to configure storage partitioning prior to connecting multiple hosts.
Operating systems such as Windows will write their signatures to any device it can access.
Heterogeneous host support means that the host systems can run various operating
systems. But be aware that all host systems within a particular storage partition have
unlimited access to all logical drives assigned to the partition. Therefore, file systems or disk
structure on these logical drives must be compatible with host systems. To ensure this, it is
best to run the same operating system on all hosts within the same partition. In certain
special cases it may be needed to run operating systems which will be able to mount foreign
file systems and share logical drives. In these cases care should be taken to ensure the
partition members are properly defined and configured to share.
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
A
host group is a collection of hosts that are allowed to access certain logical drives, for
example, a cluster of two systems.
A
host is a single system that can be mapped to a logical drive.
A
host port is the FC port of the host bus adapter (HBA) on the host system. The host port is
identified by its world-wide name (WWN). A single host can contain more than one host port.
If the servers are attached using full redundancy, 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 must be able to access both DS3500 controllers, which
can be achieved by SAN zoning.
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