IBM DS8700, Введение и руководство по планированию

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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, an extent is 1 GB. If you work in an IBM System z
environment, an extent is the size of an IBM 3390 Mod 1 disk drive.
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 together 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 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, but these 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. By identifying different volume groups for different uses or
functions (for example, SCSI target, FICON/ESCON control unit, 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 16 on page 69 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. With
the Quick Initialization feature for open system on CKD TSE and FB ESE or TSE
volumes, an internal volume initialization process allows quicker access to logical
volumes that are used as host volumes and source volumes in 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 now specify LUN ID numbers through the graphical user interface (GUI)
for volumes in a map-type volume group. Do this when you 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 could 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 is expanded from the previous maximum of 16.
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Introduction and Planning Guide