Paging space devices on systems that are managed by an HMC

Learn about the location requirements, size requirements, and redundancy preferences for paging space devices on systems that are managed by a Hardware Management Console (HMC).

When you configure the shared memory pool, you assign can paging space devices to the shared memory pool. Paging space devices can be located in physical storage in the server or on a storage area network (SAN) as follows:

  • Paging space devices that are accessed by a single Virtual I/O Server (VIOS) logical partition (hereafter referred to as a paging VIOS partition) can be located in physical storage in the server or on a SAN.
  • Paging space devices that are accessed redundantly by two paging VIOS partitions, or common paging space devices, must be located on a SAN.

When you activate a shared memory partition, the HMC allocates a paging space device (that is assigned to the shared memory pool) to the shared memory partition. The HMC allocates only one paging space device to a shared memory partition at a time. When you shut down a shared memory partition, its paging space device becomes available to the HMC to allocate elsewhere. Thus, the fewest number of paging space devices that must be assigned to the shared memory pool is equal to the number of shared memory partitions that you plan to run simultaneously. After you create the shared memory pool, you can add or remove paging space devices to or from the shared memory pool as needed.

The HMC assigns paging space devices to shared memory partitions based on the size requirements for the shared memory partition and the redundancy preferences that you specify for partition activation.

Size requirements

The HMC allocates a paging space device to a shared memory partition that best fits the size requirements of the shared memory partition.

  • For AIX® and Linux® shared memory partitions, the paging space device must be at least the size of the maximum logical memory size of the shared memory partition.
  • For IBM® i shared memory partitions, the paging space device must be at least the size of the maximum logical memory size of the shared memory partition plus 8 KB for every megabyte.

Shared memory partitions might have several partition profiles that specify different maximum logical memory sizes. To maintain flexibility, consider creating paging space devices that are large enough to be used by shared memory partitions with multiple partition profiles. When you activate a shared memory partition with a different partition profile, the shared memory partition already has a paging space device allocated to it based on the size requirements of the previously activated partition profile. If you create a paging space device that is large enough to meet the size requirements of multiple partition profiles and you activate the shared memory partition with a different partition profile, the HMC can use the same paging space device for the newly activated partition profile. If the paging space device does not meet the size requirements of the newly activated partition profile, the HMC frees the paging space device currently allocated to the shared memory partition and allocates a different paging space device that meets the size requirements specified in the newly activated partition profile.

Redundancy preferences

The HMC allocates a paging space device to a shared memory partition that satisfies the redundancy preferences that you specify for partition activation:

  • If you specify that the shared memory partition uses redundant paging VIOS partitions, the HMC uses the following process to select a suitable paging space device for the shared memory partition:
    1. The HMC assigns a paging space device that is common and available. (A paging space device is available when it is not currently assigned to a shared memory partition and is inactive.)
    2. If the HMC cannot find a paging space device that is common and available, it reassigns a paging space device that is common and unavailable. (A paging space device is unavailable when it is active and currently assigned to a shared memory partition that is shut down.)
    3. If the HMC cannot find a paging space device that is common and unavailable, it cannot activate the shared memory partition.
  • If you specify that the shared memory partition does not use redundant paging VIOS partitions, the HMC uses the following process to select a suitable paging space device for the shared memory partition:
    1. The HMC assigns a paging space device that is independent and available. (A paging space device is independent when it is accessed by only one paging VIOS partition that is assigned to the shared memory partition.)
    2. If the HMC cannot find a paging space device that is independent and available, the HMC reassigns a paging space device that is independent and unavailable.
    3. If the HMC cannot find a paging space device that is independent and unavailable, and two paging VIOS partitions are assigned to the shared memory pool, then the HMC assigns a paging space device that is common and available. In this situation, the shared memory partition does not use redundant paging VIOS partitions even though its paging space device can be accessed by both paging VIOS partitions. Also, the partition profile need not specify the second paging VIOS partition.
    4. If the HMC cannot find a paging space device that is common and available, and two paging VIOS partitions are assigned to the shared memory pool, then the HMC reassigns a paging space device that is common and unavailable. In this situation, the shared memory partition does not use redundant paging VIOS partitions even though its paging space device can be accessed by both paging VIOS partitions. Also, the partition profile need not specify the second paging VIOS partition.
    5. If the HMC cannot find a paging space device that is common and unavailable, it cannot activate the shared memory partition.
  • If you specify that the shared memory partition use redundant paging VIOS partitions, if possible, the HMC uses the following process to select a suitable paging space device for the shared memory partition:
    1. The HMC assigns a paging space device that is common and available.
    2. If the HMC cannot find a paging space device that is common and available, it assigns a paging space device that is common and unavailable.
    3. If the HMC cannot find a paging space device that is common and unavailable, it assigns a paging space device that is independent and available to the primary paging VIOS partition. In this situation, the shared memory partition does not use redundant paging VIOS partitions and the primary paging VIOS partition is the only paging VIOS partition that is assigned to the shared memory partition.
    4. If the HMC cannot find a paging space device that is independent and available to the primary paging VIOS partition, it assigns a paging space device that is independent and unavailable to the primary paging VIOS partition. In this situation, the shared memory partition does not use redundant paging VIOS partitions and the primary paging VIOS partition is the only paging VIOS partition that is assigned to the shared memory partition.
    5. If the HMC cannot find a paging space device that is independent and unavailable to the primary paging VIOS partition, it assigns a paging space device that is independent and available to the secondary paging VIOS partition. In this situation, the shared memory partition does not use redundant paging VIOS partitions and the secondary paging VIOS partition is the only paging VIOS partition that is assigned to the shared memory partition.
    6. If the HMC cannot find a paging space device that is independent and available to the secondary paging VIOS partition, it assigns a paging space device that is independent and unavailable to the secondary paging VIOS partition. In this situation, the shared memory partition does not use redundant paging VIOS partitions and the secondary paging VIOS partition is the only paging VIOS partition that is assigned to the shared memory partition.
    7. If the HMC cannot find a paging space device that is independent and unavailable to the secondary paging VIOS partition, it cannot activate the shared memory partition.