You can create a 1 TB IBM Z CKD volume. A IBM 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 IBM Z CKD volume, you must specify the number of
cylinders that you want for the volume. The storage system and the z/OS have
limits for the CKD EAV sizes. You can define CKD volumes with up to 1,182,006
cylinders, about 1 TB on the DS8880.
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
Quick initialization improves device initialization speed and allows a Copy
Services relationship to be established after a device is created.
Quick volume initialization for IBM Z environments is supported. This support
helps users who frequently delete volumes by reconfiguring capacity without
waiting for initialization. Quick initialization initializes the data logical tracks or
block 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.
Chapter 2. Hardware features
35
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