Logical configuration with DS CLI

Before you configure your storage system with the DS CLI, it is important to understand the 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 1 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 and Copy relationships. This process dynamically initializes logical volumes when they are created or expanded, allowing them to be configured and placed online more quickly.

You can specify LUN ID numbers through the graphical user interface (GUI) for volumes in a map-type volume group. You can create a new volume group, add volumes to an existing volume group, or add a volume group to a new or existing host. Previously, gaps or holes in LUN ID numbers might result in a "map error" status. The Status field is eliminated from the volume groups main page in the GUI and the volume groups accessed table on the Manage Host Connections page. You can also assign host connection nicknames and host port nicknames. Host connection nicknames can be up to 28 characters, which is expanded from the previous maximum of 12. Host port nicknames can be 32 characters, which are expanded from the previous maximum of 16.

Figure 1. Logical configuration sequence
Logical configuration consists of creating arrays, ranks, extents, volumes, and volume groups