System information

Chapter 1. Introduction to LPAR on IBM System i5 27
1.4.5 Memory allocation for the i5 OS logical partition
The logical partition is assigned a minimum, desired, and maximum memory as defined in the
logical partition profile. The memory assigned to i5 OS logical partition is only for the logical
partition. It does not include the memory reserved for Hardware Page Table (HPT). For
example, the logical partition will receive full 1024 GB of memory as configured in the logical
partition profile. Additional memory for HPT is allocated separately by the Power Hypervisor.
In previous iSeries servers, the memory allocation for a logical partition includes memory
allocated for HPT.
The virtual I/O resources also require some amount of Power Hypervisor memory, but this
only requires a small amount of memory. It only changes in 16 MB increments on the current
i5 systems.
To configure logical partition memory, determine the minimum, desired, and maximum
memory for the logical partition. Desired memory is the amount of memory configured for the
logical partition. This is the memory which the logical partition needs to have when the logical
partition is powered on. If the managed system does not have the desired amount of memory
but only has lesser memory, those uncommitted memory resources will be assigned to the
logical partition when the logical partition is activated.
Minimum memory is the minimum amount of memory which needed by the logical partition to
start. The logical partition will fail to start if the minimum memory is not available in the
system. The current memory for the logical partition cannot be lower than the configured
minimum memory. If you change the minimum memory setting for a powered on logical
partition, it will take effect after the next logical partition restart.
Maximum memory is the total amount of memory that can be allocated to this logical partition.
You can allocate additional memory to this logical partition using Dynamic Logical Partitioning
(DLPAR), but it must not exceed the maximum memory value. Figure 1-23 shows an example
of how to configure the memory in the logical partition profile.
Figure 1-23 Configure memory for logical partition