IBM DS8880 Series, Introduction And Planning Manual

Page: 41 / 244

FB volumes can only accept I/O from the host ports of hosts that are mapped to
the volumes. Host ports are zoned to communicate only with certain I/O ports on
the storage system. Zoning is configured either within the storage system by using
I/O port masking, or on the switch. Zoning ensures that the workload is spread
properly over I/O ports and that certain workloads are isolated from one another,
so that they do not interfere with each other.
The workload enters the storage system through I/O ports, which are on the host
adapters. The workload is then fed into the processor nodes, where it can be
cached for faster read/write access. If the workload is not cached, it is stored on
the arrays in the storage enclosures.
Logical configuration with DS CLI
Before you configure your storage system with the DS CLI, it is important to
understand IBM terminology for storage concepts and the storage hierarchy.
In the storage hierarchy, you begin with a physical disk. Logical groupings of eight
disks form an array site. Logical groupings of one array site form an array. After
you define your array storage type as CKD or fixed block, you can create a rank. A
rank is divided into a number of fixed-size extents. If you work with an
open-systems host, a large extent is 1 GiB, and a small extent is 16 MiB. If you
work in an IBM Z environment, a large extent is the size of an IBM 3390 Mod 1
disk drive (1113 cylinders), and a small extent is 21 cylinders.
After you create ranks, your physical storage can be considered virtualized.
Virtualization dissociates your physical storage configuration from your logical
configuration, so that volume sizes are no longer constrained by the physical size
of your arrays.
The available space on each rank is divided into extents. The extents are the
building blocks of the logical volumes. An extent is striped across all disks of an
array.
Extents of the same storage type are grouped to form an extent pool. Multiple
extent pools can create storage classes that provide greater flexibility in storage
allocation through a combination of RAID types, DDM size, DDM speed, and
DDM technology. This configuration allows a differentiation of logical volumes by
assigning them to the appropriate extent pool for the needed characteristics.
Different extent sizes for the same device type (for example, count-key-data or
fixed block) can be supported on the same storage unit. The different extent types
must be in different extent pools.
A logical volume is composed of one or more extents. A volume group specifies a
set of logical volumes. Identify different volume groups for different uses or
functions (for example, SCSI target, remote mirror and copy secondary volumes,
FlashCopy targets, and Copy Services). Access to the set of logical volumes that are
identified by the volume group can be controlled. Volume groups map hosts to
volumes. Figure 10 on page 31 shows a graphic representation of the logical
configuration sequence.
When volumes are created, you must initialize logical tracks from the host before
the host is allowed read and write access to the logical tracks on the volumes. The
Quick Initialization feature for open system on FB ESE volumes allows quicker
access to logical volumes. The volumes include host volumes and source volumes
that can be used Copy Services relationships, such as FlashCopy or Remote Mirror
Chapter 1. Overview
29