Memory

Processors use memory to temporarily hold information. Memory requirements for logical partitions depend on the logical partition configuration, I/O resources assigned, and applications used.

Memory can be assigned in increments of 16 MB, 32 MB, 64 MB, 128 MB, and 256 MB. The default memory block size varies according to the amount of configurable memory in the system.

There are limits on how large a logical partition can grow based on the amount of memory initially allocated to it. Memory is added and removed to and from logical partitions in units of logical memory blocks. For logical partitions that are initially sized less than 256 MB, the maximum size to which a logical partition can grow is 16 times its initial size (up to the assigned maximum memory of the logical partition). For logical partitions that are initially sized 256 MB or larger, the maximum size to which the logical partition can grow is 64 times its initial size (up to the assigned maximum memory of the logical partition). The smallest increment for adding or removing memory to or from a logical partition is 16 MB.

The memory block size can be changed by using the Integrated Virtualization Manager, or the Logical Memory Block Size option in the Advanced System Management Interface (ASMI). The machine default value should only be changed under direction from your service provider. To change the memory block size, you must be a user with administrator authority, and you must shut down and restart the managed system for the change to take effect. If the minimum memory amount in any partition profile on the managed system is less than the new memory block size, you must also change the minimum memory amount in the partition profile.

Each logical partition has a hardware page table (HPT). The HPT ratio is the ratio of the HPT size to the maximum memory value for the logical partition. The HPT is allocated in the server firmware memory overhead for the logical partition, and the size of the HPT can affect the performance of the logical partition. The size of the HPT is determined by the following factors:

• The HPT ratio of 1/64 is the default value for IBM® i logical partitions, and 1/128 for AIX® and Linux logical partitions.
  Note: You can override the default value by using the HMC command-line interface to change the value in the partition profile.
• The maximum memory values that you establish for the logical partition (dedicated or shared)

On systems that are managed by a Hardware Management Console, memory is assigned to logical partitions using partition profiles. On systems that are managed by the Integrated Virtualization Manager, memory is assigned to logical partitions using the partition properties.