IBM AIX HACMP, Руководство пользователя по оборудованию

Страница: 52 / 240

34
IBM Certification Study Guide AIX HACMP
Here the resource groups are the same as the ones in the mutual takeover
configuration. Also, similar to the previous configuration, nodes 1 and 2 each
have priorities of 1 for one of the resource groups, A or B. The only thing
different in this configuration is that there is a third node which has a priority
of 2 for both the resource groups.
During normal operations, node 3 is either idle or is providing non-critical
services. In the case of either node 1 or node 2 failing, node 3 takes over the
failed node’s resource groups and starts providing its services. When a failed
node rejoins the cluster, it reacquires the resource group for which it has the
highest priority.
So, in this configuration, you are protected against the failure of two nodes
and there is no performance degradation after the failure of one node.
2.4.2.2 Concurrent Disk Access Configurations
A concurrent disk access configuration usually has all its disk storage defined
as part of one concurrent resource group. The nodes associated with a
concurrent resource group have no priorities assigned to them.
If a 7135 RAIDiant Array Subsystem is used for storage, you can have a
maximum of four nodes concurrently accessing a set of storage resources. If
you are using the 7133 SSA Disk Subsystem, you can have up to eight nodes
concurrently accessing it.This is because of the physical characteristics of
SCSI versus SSA.
In the case of a node failure, a concurrent resource group is not explicitly
taken over by any other node, since it is already active on the other nodes.
However, in order to somewhat mask a node failure from the end users, you
should also have cascading resource groups, each containing the service IP
address for each node in the cluster. When a node fails, its service IP
address will be taken over by another node and users can continue to access
critical services at the same IP address that they were using before the node
failed.
2.4.3 IP Address Takeover
The goal of IP Address Takeover is to make the server’s service address
highly available and to give clients the possibility of always connecting to the
same IP address. In order to achieve this, you must do the following:
• Decide which types of networks and point-to-point connections to use in
the cluster (see 2.2, “Cluster Networks” on page 11 for supported network
types)