Sharing resources between logical partitions

Although each logical partition acts as an independent server, the logical partitions on a server can share some kinds of resources with each other. The ability to share resources among many logical partitions allows you to increase resource utilization on the server and to move the server resources to where they are needed.

The following list illustrates some of the ways in which logical partitions can share resources. For some server models, the features mentioned in this list are options for which you must obtain and enter an activation code:

• The Micro-Partitioning® technology (or shared processing) allows logical partitions to share the processors in shared processor pools. Each logical partition that uses shared processors is assigned a specific amount of processor power from its shared processor pool. By default, each logical partition is set so that the logical partition uses no more than its assigned processor power. Optionally, you can set a logical partition so that the logical partition can use processor power that is not being used by other logical partitions in its shared processor pool. If you set the logical partition so that it can use unused processor power, the amount of processor power that the logical partition can use is limited by the virtual processor settings of the logical partition and by the amount of unused processor power available in the shared processor pool that is used by the logical partition.
• Logical partitions can share the memory in the shared memory pool by using the PowerVM® Active Memory™ Sharing technology (or shared memory). Instead of assigning a dedicated amount of physical memory to each logical partition that uses shared memory (hereafter referred to as shared memory partitions), the hypervisor constantly provides the physical memory from the shared memory pool to the shared memory partitions as needed. The hypervisor provides portions of the shared memory pool that are not currently being used by shared memory partitions to other shared memory partitions that need to use the memory. When a shared memory partition needs more memory than the current amount of unused memory in the shared memory pool, the hypervisor stores a portion of the memory that belongs to the shared memory partition in auxiliary storage. Access to the auxiliary storage is provided by a Virtual I/O Server logical partition. When the operating system attempts to access data that is located in the auxiliary storage, the hypervisor directs a Virtual I/O Server to retrieve the data from the auxiliary storage and write it to the shared memory pool so that the operating system can access the data. The PowerVM Active Memory Sharing technology is available with the PowerVM Enterprise Edition hardware feature, which also includes the license for the Virtual I/O Server software.
• The Dynamic partitioning feature allows you to manually move resources to, from, and between running logical partitions without shutting down or restarting the logical partitions. This allows you to share devices that logical partitions use occasionally. For example, if the logical partitions on your server use an optical drive occasionally, you can assign a single optical drive to multiple logical partitions as a desired device. The optical drive would belong to only one logical partition at a time, but you can use dynamic partitioning to move the optical drive between logical partitions as needed. Dynamic partitioning is not supported on servers that are managed using the Virtual Partition Manager.
• Virtual I/O allows logical partitions to access and use I/O resources on other logical partitions. For example, virtual Ethernet allows you to create a virtual LAN that connects the logical partitions on your server to each other. If one of the logical partitions on the server has a physical Ethernet adapter that is connected to an external network, you can configure the operating system of that logical partition to connect the virtual LAN with the physical Ethernet adapter. This allows the logical partitions on the server to share a physical Ethernet connection to an external network.
• A Host Ethernet Adapter (HEA), or Integrated Virtual Ethernet (IVE), allows multiple logical partitions on the same server to share a single physical Ethernet adapter. Unlike most other types of I/O devices, you can never assign the HEA itself to a logical partition. Instead, multiple logical partitions can connect directly to the HEA and use the HEA resources. This allows these logical partitions to access external networks through the HEA without having to go through an Ethernet bridge on another logical partition.
• The single root I/O virtualization (SR-IOV) specification defines extensions to the PCI Express® (PCIe) specification. SR-IOV allows virtualization of the physical ports of an adapter so that the ports can be shared by multiple partitions that are running simultaneously. For example, a single physical Ethernet port appears as several separate physical devices.