Logical partition concept: Memory
Processors use memory to temporarily hold information. Memory requirements for partitions are dependent on partition configuration, I/O resources assigned, and applications used.
When you create a partition, add a whole number of megabytes of memory to it (1 MB = 1024 x 1024 bytes). The primary partition needs a minimum of 256 MB of memory. Depending on configuration values used, a primary partition may require more than 256 MB. Secondary partitions running V4R4 and V4R5 require a minimum value of 64MB. Secondary partitions running V5R1 and V5R2 require a minimum of 128 MB of memory. Depending on configuration values used, a secondary partition may require more than 128 MB.
Memory in each logical partition operates within its assigned minimum and maximum values. You can dynamically move memory between V5R1 and V5R2 logical partitions without needing to restart the affected partitions as long as your request for memory movement is within the range of the minimum and maximum values specified during partition creation. When you request to dynamically move memory between partitions, note that this memory is removed and added to the base memory pool of each of the partitions (*BASE pool). Private memory pools or shared memory pools are not affected. If the move request exceeds the amount of memory available in the base pool, the system will only free up excess memory pages after keeping the minimum amount of memory required in the base pool. This value is determined by the base storage minimum size (QBASPOOL) system value. To prevent any data loss during memory movement, the system first writes any data from memory pages to the disks before making the memory pages available to another partition. Depending on the amount of memory you have requested to move, this may take some time.
Each partition will report its runtime minimum memory size. This value is an estimate of how much memory in the partition is locked into that partition and cannot be moved dynamically. Reducing the number of processes or threads within a partition or changing the *BASE pool will affect the runtime minimum.
The full amount of memory that you assign to a logical partition may not be available for the partition's use. Static memory overhead required to support the assigned maximum memory will affect the reserved or hidden memory amount. This static memory overhead will also influence the minimum memory size of a partition.
The minimum memory size assigned to a partition can be changed with only a restart of the partition. However, changes to the maximum memory size require a restart of the entire system and may require a larger minimum memory value.
If there is a memory failure, the system will attempt to accommodate the minimums for all partitions. If all minimums are satisfied, the secondary partitions will restart with all additional resources distributed proportionally to their allocation. If all minimums are not satisfied, the system will put all resources in the primary and fail to restart with the partition configuration protected and a product activity log (PAL) error of B6005343. You can view memory errors in the PAL on the primary partition.
Parent topic:
Hardware for logical partitionsRelated concepts
Logical partition concept: Bus Logical partition concept: Processor Restarting and powering down a system with logical partitions