Dynamically switching IOPs between partitions

A powerful advantage of logical partitions is ability to dynamically switch an IOP from one partition to another.

When you dynamically switch an IOP, you take the control of an IOP away from one partition and give it to another without restarting the server.

On a shared bus, IOPs and their resources (all IOAs and attached devices) can be dynamically moved between partitions. To initiate this action, right click on the desired IOP and select Move.

When you dynamically switch an IOP between partitions, you make it appear as though partitions can share devices. For example, if your server has a low use device, more than one partition can use that device by switching IOPs. Each partition can use the device because switching an IOP switches all devices attached to it. However, partitions can only use that device one at a time. You can only switch the IOP to one partition at time. Before you perform this task, you need to free that device in i5/OS™ on the source partition. You can do this by using the iSeries™ Navigator.

IOPs that are candidates for switching include:

• IOPs that control high cost devices.
• IOPs that control low use devices and low demand devices.
• IOPs that solely control the target device or devices.

Before you use IOP switching, you should remember the IBM^® recommended approach to logical partitioning is to dedicate all hardware within a partition. You should partition your server at the bus level. However, when you use bus level partitioning you cannot switch IOPs. Also, bus level partitioning is not always cost-effective. Therefore, you may find it preferable to share some devices among partitions. And while partitions cannot concurrently share devices, IOP switching may be an effective solution to the cost problem.

Before you implement switching, you should consider other possible alternatives. To share devices among partitions, you can apply the same techniques that are used to share devices among separate physical systems:

• Use multiple IOPs, one in each partition, for devices that support multiple connections (some high end tape drives).
• Use multiple IOPs, one in each partition, and a switch box for devices that only support single connections (printers, or some high end tape drives).
• Use multiple IOPs and multiple devices in each partition for a self-contained solution (internal removable media devices).
• If it is not feasible for you to use any of these alternatives, then you should implement IOP switching.

You can implement dynamic IOP switching by making sure that the primary partition owns each bus with a bus ownership type of own bus shared. All secondary partitions can then simply use any bus they need. With this configuration you can assign every IOP in the server to the partition that wants to use it. All partitions can dynamically add and remove any IOPs that control high cost, and low use devices that are attached to the system.

In addition to enabling IOP switching, this configuration has several other advantages.

• Conceptually, the implementation is easy to configure and understand.
• The primary partition will own any new hardware that is added to the system.
• As partition needs change over time, you can make adjustments with optimal hardware use and greater flexibility.