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Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

When using the AIX 5L as the operating system, there are two combinations possible:

* Raw devices with the use of HACMP/ES CRM 4.4.x cluster OSD.

* GPFS ? General Parallel File System with the use of HACMP/ES 4.4.x OSD.

The IBM High Availability Cluster Multi-Processing for AIX (HACMP) Version 4.4.x has been in use for quite sometime. HACMP is designed to detect system failures and manage failover, where necessary, to a recovery processor with a minimal loss of end-user time. HACMP 4.4.x offers improved usability, more flexible installation options, and additional hardware and software support for RS/6000 customers with mission critical applications.

We examine the RAC setup in two ways:

*   Using the VSD using PSSP on RS/6000 SP systems.

*   Using HACMP/ES on RS/6000 and pSeries machines.

The VSD are to be used with a SP machine running AIX 4.3.3, and PSSP 3.2. PSSP stands for IBM?s Parallel System Support Programs. The HACMP/ES is used for the clusters of pSeries machines with AIX 4.3.3 and above.

What is VSD?

The IBM VSD (Virtual Shared Disk) software is a component of PSSP that allows data on disks attached to some SP nodes to be shared with other nodes using a high-speed interconnect network like SP Switch or SP Switch2. The Parallel System Support Programs (PSSP) software provides a comprehensive suite of applications for the installation, operation, management, and administration of the RS/6000 SP attached servers and Clustered Enterprise Servers (CES) from a single point of control.

The VSD is a logical volume that can be accessed both by the node to which it belongs and also by other nodes in the system. The VSD nodes that share data may reside in a single system partition. VSD software allows applications running on different nodes to have access to raw logical volumes as if they were local. I/O requests to VSD(s) are routed by the VSD device driver, which is loaded as a kernel extension on each node, thus making raw logical volumes accessible to other nodes in the system.

Depending on the VSD function, a node can be:

* VSD Server that has the local attached disks. It is able to complete I/O requests from VSD clients by using a communication network inside the system.

* A VSD Client that is a node requesting access to VSD(s).

There is another variation for VSD, which is known as Concurrent VSD. The Concurrent Virtual Shared Disk feature of PSSP allows multiple VSD servers to simultaneously access logical volumes inside a volume group using the Concurrent Logical Volume Manager (CLVM) component supplied by AIX. I/O requests from nodes that do not have locally attached disks are spread across VSD servers, thus improving raw logical volume access.

When using the Concurrent Virtual Shared Disk, recovery from node failure is much faster because the failed node is marked as unavailable to all other nodes. Its access to the physical disk is fenced, while the other nodes can continue to access the disks. Virtual Shared Disks provide access to non-local disks. They behave like raw logical volumes. They can be configured using SMIT or commands. VSD(s) are accessed through the SP Switch so the network overhead is very low.

The HACMP method may involve the use of concurrent logical volume groups. The HACMP layer includes the concurrent logical volume manager (CLVM). HACMP/ES installation has many steps, which include:

* Installing and setting up the hardware.

* Installing the AIX operating system.

* Installing the latest maintenance and required patches.

* Installing the HACMP/ES on each node and applying patches.


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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