IBM DS8880 Series, Introduction And Planning Manual

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Arrays
An array, also referred to as a managed array, is a group of storage devices
that provides capacity for a pool. An array generally consists of 8 drives
that are managed as a Redundant Array of Independent Disks (RAID).
Pools A storage pool is a collection of storage that identifies a set of storage
resources. These resources provide the capacity and management
requirements for arrays and volumes that have the same storage type,
either fixed block (FB) or count key data (CKD).
Volumes
A volume is a fixed amount of storage on a storage device.
LSS The logical subsystem (LSS) that enables one or more host I/O interfaces to
access a set of devices.
Hosts
A host is the computer system that interacts with the storage system. Hosts
defined on the storage system are configured with a user-designated host
type that enables the storage system to recognize and interact with the
host. Only hosts that are mapped to volumes can access those volumes.
Logical configuration of the storage system begins with managed arrays. When
you create storage pools, you assign the arrays to pools and then create volumes in
the pools. FB volumes are connected through host ports to an open systems host.
CKD volumes require that logical subsystems (LSSs) be created as well so that they
can be accessed by an IBM Z host.
Pools must be created in pairs to balance the storage workload. Each pool in the
pool pair is controlled by a processor node (either Node 0 or Node 1). Balancing
the workload helps to prevent one node from doing most of the work and results
in more efficient I/O processing, which can improve overall system performance.
Both pools in the pair must be formatted for the same storage type, either FB or
CKD storage. You can create multiple pool pairs to isolate workloads.
When you create a pair of pools, you can choose to automatically assign all
available arrays to the pools, or assign them manually afterward. If the arrays are
assigned automatically, the system balances them across both pools so that the
workload is distributed evenly across both nodes. Automatic assignment also
ensures that spares and device adapter (DA) pairs are distributed equally between
the pools.
If you are connecting to a IBM Z host, you must create a logical subsystem (LSS)
before you can create CKD volumes.
You can create a set of volumes that share characteristics, such as capacity and
storage type, in a pool pair. The system automatically balances the volumes
between both pools. If the pools are managed by Easy Tier, the capacity in the
volumes is automatically distributed among the arrays. If the pools are not
managed by Easy Tier, you can choose to use the rotate capacity allocation method,
which stripes capacity across the arrays.
If the volumes are connecting to a IBM Z host, the next steps of the configuration
process are completed on the host.
If the volumes are connecting to an open systems host, map the volumes to the
host, add host ports to the host, and then map the ports to the I/O ports on the
storage system.
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DS8880 Introduction and Planning Guide