The SP can have a variety of both hardware and software resources associated with it. This section discusses how these resources interact with each other with regard to system partitions.
You manage a partitioned SP system from a single point of control using the control workstation. There is one common administrative domain from which you can restrict interaction to one system partition.
From an administrative point of view, each partition is a logical SP system within one common administrative domain. This means that:
The entire SP is one administrative domain for the system administrator, who manages the system partitions as logical SP systems. An administrator restricts interaction to a specific system partition by setting the SP_NAME environment variable to the name or IP address of that system partition.
On the control workstation, the administrator is in an environment for one system partition at a time, as defined by the SP_NAME environment variable. Any task performed at the control workstation that requires information from the SDR gets the information for the current system partition. The operator must either set the SP_NAME environment variable or issue a command that sets it. If SP_NAME is not set, the environment is the default (or persistent) system partition.
The SDR contains data about the entire SP system. Generally, this data is separated into system (global) and partitioned classes. Requests made to the SDR, whether in software or manually, require an appropriate name or IP address for the system partition. If no such identifier is specified, the value of SP_NAME is used.
On the control workstation, the administrator is in an environment for one system partition at a time as identified by the SP_NAME environment variable. Any task performed at the control workstation that gets information from the SDR gets the information for the current system partition. Also, all global data (data affecting all system partitions) is accessible from any system partition.
System partitioning does not require physical changes to the networking configurations of a system. You should consider certain effects that might warrant a physical change.
Ethernet interference, causing slower performance, might occur between nodes on the same physical Ethernet subnetwork. If these nodes are in different system partitions, an action such as booting all the nodes in one system partition might adversely affect the other system partition. You should consider creating system partitions aligned on the physical Ethernet subnetwork boundaries. This is fairly straightforward for system partitioning where the partitioning is on frame boundaries.
There is no connectivity over the switch between system partitions. This means that a gateway node with routing set up to the switch network might require routing changes if the gateway is to remain a gateway for more than one system partition. You can do this using explicit host routes on the gateway node, or by enabling ARP on all system partitions and redefining the IP addresses within a system partition as a different subnetwork.
Remember that a system partition is an SP system -- essentially a smaller SP carved out of the whole one. You cannot expect the smaller SP to do what the larger cannot. However, more flexibility was introduced with coexistence to support migration and make it easier to upgrade production applications.
With coexistence, nodes can still be divided into partitions. However, coexistence lets each node within that partition run its own individual version of PSSP. Within that node, any software that operates under that node's version of PSSP will still function. Even though the nodes are running a variety of PSSP levels, the SP system still functions normally. Therefore, depending on migration and coexistence limitations of the software you have or plan to install, you might be able to migrate your SP system one node at a time.
For additional information on this support, including supported levels and limitations, see Chapter 11, "Planning for migration".
The SP resources must conform to certain rules if they are to be a part of a system partition. The following list provides an overview of these rules:
A physical file system, that is, the logical volumes containing the files, cannot span system partitions.
The physical types supported in the SP system for running PSSP are: thin, wide, and high nodes in SP frames, and SP-attached servers. The physical type affects the membership possibilities in a system partition. To understand how you can run multiple node types within a system partition, you need to understand the concepts of node slots and switch chips. A node slot is the space that one thin node can occupy in an SP frame. Every node or SP-attached server gets connected to one port on the switch chip.
There are 16 node slots in an SP frame. Figure 33 shows how the slots are numbered in a frame. In Example 1, we considered a 1-frame system of 16 thin nodes. In that case, there is one node per slot, and the number of a node is precisely the number of the slot it occupies.
Figure 33. One SP frame with slots numbered
A wide node occupies two adjacent slots (a drawer) and a high node occupies four adjacent slots (2 adjacent drawers). The correspondence between node numbers and slot numbers is a topic of Example 3. For now, remember a node's node number is the lowest numbered slot that it occupies. As you plan your system partitions, think in terms of slots. Then you can decide what combination of thin, wide, and high nodes you want to occupy those slots.
Figure 34 shows a frame populated with 3 wide, 1 high, and 6 thin nodes. The nodes in that figure have been given simple names using their node number. Note that nodes 2, 8, 10, 11, 12, and 14 do not exist. The preceding discussion expands to the following complete summary for the slots of the frame in Figure 33:
Figure 34. Varied nodes, 1-frame SP system
In a switched SP, the switch chip is the basic building block of a system partition: if a switch chip is placed in a partition, then any nodes connected to that chip's node switch ports are members of that partition, also. So, any system partition in a switched SP is physically comprised of switch chips, any nodes attached to ports on those chips, and the links that join those nodes and chips.
A system partition can be no smaller than a switch chip and the nodes attached to it which occupy some number of slots in the SP system. Following are examples of possible scenarios of nodes attached to a single switch chip:
In practice, every slot is assigned to some chip, via fictitious nodes if necessary, so that if that slot is later filled with a node, it is not a major reconfiguration event.
An SP-attached server is not in an SP frame, but it is managed by the PSSP components as though it is in a frame. The SP-attached server is always viewed as occupying slot one in its frame. Its frame is considered to have 16 node slots, just like SP frames. However, because it must attach to an existing SP frame, it must occupy a port in the switch chip whether or not it also connects to an SP Switch.