Central storage origin

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There must be enough contiguous central storage addressability to fit the reserved amounts, but the reserved amounts can be in use by other LPs (that specified origins for storage) at the time the LP is activated.
The origin for central storage defines the starting gigabyte where the central storage addressability range begins for the LP. If enough storage is not available to satisfy the initial central storage request starting at this origin, LP activation will fail.
For central storage, the specification of the origin parameter provides the only way to overlap storage definitions. For example, the reserved storage definition for one LP can overlap the storage definition of another LP when the origin parameter is specified for both LPs.
The total amount of central storage addressability that can be used to map central storage for LPs is at least twice the amount of customer storage. You can review current LP storage allocations by using the Storage Information task available.
Since the specification of a central storage origin is optional, there are two implementations of dynamic storage reconfiguration for reserved central storage:
1. If you do not specify a central storage origin, the reserved central storage is available for the LP when there is sufficient physical storage available to meet the reserved central storage request.
  Storage can be reassigned between LPs that have noncontiguous address ranges. Reconfiguration is not limited to growing into an adjacent LP. LPs are eligible to use noncontiguous central storage if they have unique (not overlapping) storage range definitions. Specifying an origin is not required when defining a reserved storage amount for an LP, and by not specifying an origin, the LP is reserved an addressable storage range for its entire storage configuration (initial plus reserved amount). Not specifying an origin ensures no overlap. The reserved central storage is available for LPs that do not specify an origin when there is sufficient physical storage to meet the reserved central storage request.
2. If you specify a central storage origin, the entire reserved central storage amount is only available for the LP when:
  - No other LP has this central storage address range, to which the reserved central storage is mapped, online.
  - There is sufficient physical storage available to meet the reserved central storage request.
If no origin is specified for an LP, the system assigns the storage to the LP using a top-down first-fit algorithm. Storage that is part of reserved central storage for another activated LP is not available for any LPs that do not specify a central storage origin. The addressing for each logical partition must start and end on a 2 GB boundary. If the INITIAL or non-zero RESERVED amounts defined for a logical partition with no origin specified are not multiples of 2 GB, the addressing allocated for each of these specifications will be rounded up to 2 GB boundaries. This will be reflected to the partition in the amount of offline central storage for the partition.
For example, define a logical partition with 5 GB of INITIAL, 0 MB of RESERVED, and a system determined central storage origin. The 5GB requires a 1 GB granularity for allocation here but to meet the 2 GB addressing needs for the central storage, 6 GB of addressing is required for this logical partition. A single online central storage element is created with provisions for 6 GB of central storage but only the original 5 GB is actually allocated to the logical partition at activation time. The additional 1 GB could potentially be configured online for use at a later time via appropriate OS commands. The Figure 1 displays what the z/OS D M=STOR command would display when this logical partition is first activated with this configuration.
Figure 1. Example of z/OS D M=STOR command output
```
D M=STOR
IEE174I 10.00.09 DISPLAY M 399
REAL STORAGE STATUS
ONLINE-NOT RECONFIGURABLE
			OM-5120M
ONLINE-RECONFIGURABLE
			NONE
PENDING OFFLINE
			NONE
		OM IN OFFLINE STORAGE ELEMENT(S)
		1024M UNASSIGNED STORAGE
STORAGE INCREMENT SIZE IS 1024M						 
```