IBM DS8700, Введение и руководство по планированию

Страница: 62 / 256

A System z CKD volume is composed of one or more extents from a CKD extent
pool. CKD extents are 1113 cylinders in size. When you define a System z CKD
volume, you must specify the number of cylinders that you want for the volume.
The DS8000 and the zOS have limits for the CKD EAV sizes. You can define CKD
volumes with up to 262,668 cylinders, about 223 GB on the DS8700 and 1,182,006
cylinders, about 1 TB on the DS8800.
If the number of cylinders that you specify is not an exact multiple of 1113
cylinders, then some space in the last allocated extent is wasted. For example, if
you define 1114 or 3340 cylinders, 1112 cylinders are wasted. For maximum storage
efficiency, consider allocating volumes that are exact multiples of 1113 cylinders. In
fact, multiples of 3339 cylinders should be considered for future compatibility. If
you want to use the maximum number of cylinders for a volume (that is 1,182,006
cylinders), you are not wasting cylinders, because it is an exact multiple of 1113
(1,182,006 divided by 1113 is exactly 1062). This size is also an even multiple (354)
of 3339, a model 3 size.
Quick initialization
The quick initialization function initializes the data logical tracks or blocks within a
specified extent range on a logical volume with the appropriate initialization
pattern for the host.
Normal read and write access to the logical volume is allowed during the
initialization process. Therefore, the extent metadata must be allocated and
initialized before the quick initialization function is started. Depending on the
operation, the quick initialization can be started for the entire logical volume or for
an extent range on the logical volume.
The quick initialization function is started for the following operations:
v Standard logical volume creation
v
Standard logical volume expansion
v Standard logical volume reinitialization
v
Extent space-efficient (ESE) logical volume expansion
v ESE logical volume reinitialization
v ESE logical volume extent conversion
v
Track space-efficient (TSE) or compressed TSE logical volume expansion
v TSE or compressed TSE logical volume reinitialization
40
Introduction and Planning Guide