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Predrag Simović
Asked: 2011-08-23 12:32:00 +0800 CST

Oracle RAC failover backup procedure

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We have Oracle 11gR2 RAC database on two nodes. We also have a RMAN backup script that works fine, using a recovery catalog database which is located in a town 20km from the data center. The script for database backup works fine, and is started from crontab Job or from Oracle dbconsole (for now it works from crontab). A recovery procedure is checked and everything is working properly.

The problem is that the script runs from the first node in the cluster, and if the node is turned off, backup can't be run. How can we ensure that our script have a failover backup version. We also tried to do the backup over dbconsole but this only works if the node from which to start job was started.

Essentially the question is "How to ensure that our backup works, whether or not both nodes are active"

oracle database-backup oracle-rac

2 Answers

  1. In a simple well-written RMAN script there is nothing that would prevent it from being used on a different instance of the same database, so I guess the question is really about getting rid of a single point of failure (SPOF) of invocation of such RMAN script.

    With crontab scheduling, to avoid SPOF you have to have two (or more) crontabs.

    The crude way is to always execute the backup on every node, but this wastes time and resources.

    Better solution is to have a custom script that performs the backup on the first node always, and on the second node only when it detects via crsstat that first node is OFFLINE.

    If you are good at scripting, I would arrange it as (pardon the pseudocode):

    this_host = hostname -s
alphabetical_good_hosts = ` crsstat -t | grep 'inst *ONLINE *ONLINE' | cut the hostname | sort `
if this_host != first_element_of( alphabetical_good_hosts ) ; then
    echo Silently exiting, we are not the preferred node for backup
    exit 0
endif
rman target / catalog someone@rman
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  2. Connect to the database through a database service. The service should be server pool managed and both nodes should be part of the pool. Then the service is always offered and the script wil run if any of the two nodes is up. The service can be defined with the srvctl command.

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