Processors use memory to temporarily hold information. Memory requirements for partitions depend on partition configuration, I/O resources assigned, and applications used.
Different partitioning tools assign memory to logical partitions in different ways. For more information on memory assignment by a specific partitioning tool, see Partitioning tools.
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.
| Amount of configurable memory | Default memory block size |
|---|---|
| Less than 4 GB | 16 MB |
| Greater than 4 GB up to 8 GB | 32 MB |
| Greater than 8 GB up to 16 GB | 64 MB |
| Greater than 16 GB up to 32 GB | 128 MB |
| Greater than 32 GB | 256 MB |
The memory block size can be changed by using 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.
Depending on the overall memory in your system and the maximum memory values you choose for each partition, the server firmware must have enough memory to perform logical partition tasks. Each partition has a Hardware Page Table (HPT). The size of the HPT is based on an HPT ratio of 1/64 and is determined by the maximum memory values you establish for each partition.
Server firmware requires memory to support the logical partitions on the server. The amount of memory required by the server firmware varies according to several factors. Factors influencing server firmware memory requirements include the following:
Generally, you can estimate the amount of memory required by server firmware to be approximately 8% of the system installed memory. The actual amount required will generally be less than 8%. However, there are some server models that require an absolute minimum amount of memory for server firmware, regardless of the previously mentioned considerations.
When selecting the maximum memory values for each partition, consider the following:
If the server firmware detects that a memory module is about to fail, or if a memory module fails when the memory module is not in use, then the server firmware creates a serviceable event. The server firmware can also deconfigure the failing memory module automatically, depending upon the type of failure and the deconfiguration policies that you set up using the Advanced System Management Interface (ASMI). You can also deconfigure a failing memory module manually using the ASMI.
If a memory module fails when the memory module is in use, then the entire managed system shuts down. When a memory module failure causes the entire managed system to shut down, deconfigure the failed memory module manually and restart the managed system. The managed system attempts to start the logical partitions that were running at the time of the memory module failure with their minimum memory values. If the managed system does not have enough memory to start all of the logical partitions with their minimum memory values, then the managed system starts as many logical partitions as it can with their minimum memory values. If there is any memory left over after the managed system is done starting logical partitions, then the managed system distributes any remaining memory resources to the running logical partitions in proportion to their desired memory values.