ISS Technology Update, Volume 7 Number 5 - Newsletter

ISS Technology Update Volume 7, Number 5

Table 5-1. Strengths and weaknesses of active/passive clusters

Strengths Weaknesses

• High availability with less down time than single systems.

• Secondary node can be used for separate applications during

passive mode.

• Relatively small failover time (< 30 minutes).

• Failover can be automated with cluster management tools

such as HP Serviceguard and Oracle Data Guard.

• Application licensing is often only required for a single server.

• Databases and applications have to be restarted impacting

availability and performance.

• Multiple systems have to be managed.

• Complex configuration issues occur.

• Users must reconnect or be reconnected to the second node in the

event of a failover.

• Can result in underutilized server resources.

• No instantaneous or transparent application failover.

Active/Active Clusters

In an active/active (Figure 5-2), both servers are physically connected to the storage and both can access the storage

simultaneously. This is a valuable solution for database environments. In this environment, the database vendor has to provide a

distributed lock management capability to prevent data corruption that could arise from simultaneous access from two separate

systems. Examples of this type of clustering are Oracle Real Application Clusters (RAC), RedHat GFS cluster file system, and HP

PolyServe cluster file gateway.

Figure 5-2. Active/Active Cluster Example

Table 5-2. Strengths and weaknesses of active/active clusters

Strengths Weaknesses

• High availability with less down time than single systems.

• Both nodes are active participants in the cluster.

• Very short failover time (< 90 seconds).

• Failover can be automated with cluster management tools

such as HP Serviceguard and Oracle Enterprise Manager.

• The investment of each server in the cluster is used.

• With Oracle RAC, the cluster can be dynamically expanded.

• Complex infrastructure combining many separate components

• Multiple systems to manage

• Complex configuration issues for setup and maintenance

• Licensing for both servers can result in higher application costs