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AIX 5L V5.3 and POWER5 processor-based IBM eServer® p5 systems allow the creation of a large number (up to 254) of logical partitions in a single system. While this provides many opportunities for server consolidation and for running applications in their own logical partitions to isolate them from the effects of unrelated applications, it does create a problem for access to I/O devices: each of the 254 logical partitions cannot have its own physical I/O adapters, since there are not that many I/O slots in the system.
The Advance POWER Virtualization option provides a way around this problem through its virtual I/O capability: one or more hosting partitions own the physical I/O adapters that communicate with real devices. Other ("client") partitions communicate with the hosting partition via the POWER™ Hypervisor™. The communication mechanism is designed ("virtualized") so that from the point of view of applications and most of the AIX 5L operating system, there is no distinction between the behavior of the remotely accessed device, and one that was attached to that logical partition. One of the virtual I/O facilities is called VSCSI. It provides access to disk devices.
The HACMP program product provides high availability for mission-critical applications. One of the advanced features of HACMP is the Enhanced Concurrent Mode disk access method, which improves disk recovery time independent of the detailed behavior of disk devices.
This paper describes how the enhanced concurrent mode facility of HACMP can be used to accommodate VSCSI devices.
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