IBM Z9, Planning Manual

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Recommendations for Storage Map Planning
Planning storage maps as described below will help avoid storage fragmentation
and remove dependencies on the order of activation of LPs.
For more information and examples of storage map planning, see the publications
listed for dynamic storage reconfiguration in “About This Publication” on page xvii.
v It is possible to define expanded storage to LPs in such a way that many LPs
use the same expanded storage addressability (one LP at a time). If you want
this, no more than one LP should have this expanded storage defined as its
initial expanded storage. Instead, define it as reserved expanded storage.
Note: If you do not observe this convention, it can inhibit automatic activation of
LPs.
v Map all LPs that require an origin from the bottom up (that is, start with 0 MB
and build upward). When both central and expanded storage require origins, map
the storage in the same order for both central and expanded storage.
If no origin is specified for an LP, the system assigns the storage to the LP using
a top-down first-fit algorithm for both central and expanded storage.
Operation Considerations for Dynamic Storage Reconfiguration:
v
Initial central storage for an LP is allocated on logical storage element 0 and any
reserved central is allocated on logical storage element 1.
v
Whenever a load clear or system reset clear is performed on an LP, it forces the
reserved central storage element offline. This allows z/OS to flag the reserved
storage element as reconfigurable to allow it to be later deconfigured from the
LP.
0 GB
1020 GB
1022 GB
1024 GB
RSVD = 2 GB (online)
UnusedAddressability
LP-A
INIT = 2 GB (online)
Addressable
Storage
Figure 3-13. Expanded Storage Layout Following Reconfiguration
Chapter 3. Determining the Characteristics of Logical Partitions
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