Veritas Cluster Overview

Veritas Cluster enables one system to failover to the other system. All related software processes are simply moved from one system to the other system with minimal downtime.

Veritas Cluster does NOT have both boxes up at once sevicing requests. It only offers a hot standby system. This enables the system to keep running (with a short transfer period) if a machine fails or system maintenance needs to be done.

Cluster Startup

Here is what the cluster does at startup:

Node checks if other node is already started, if so -- stays OFFLINE

If no other machine is running, checks communication (gabconfig). May need system admin intervention if cluster requires both nodes to be available. (/sbin/gabconfig -c -x)

Once communication between machines is open -- or gabconfig has been started, it sets up network (nic & ip adddress) (starts cluster server)

If also brings up volume manager, file system, and then oracle.

If any of the critical processes fail, the whole system is faulted. The most common reason for failing is expired licenses, so check licenses before doing work with vxlicense -p.

File Locations (Logs, Conf, Executables)

Log location: /var/VRTSvcs/log

There are several logs in this directory:

hashadow-log_A: hashadow checks to see if the ha cluster daemon (had) is up and restarts it if needed. This is the log of that process.

engine.log_A: primary log, usually what you will be reading for debugging

Oracle_A: oracle process log (related to cluster only)

Sqlnet_A: sqlnet process log (related to cluster only)

IP_A: related to shared IP

Volume_A: related to Volume manager

Mount_A: related to mounting actual filesystes (filesystem)

DiskGroup_A: related to Volume Manager/Cluster Server

NIC_A: related to actual network device

Look at the most recent ones for debugging purposes (ls -ltr).

Conf files:

Llt conf: /etc/llttab [should NOT need to access this]

Network conf: /etc/gabtab
If has: /sbin/gabconfig -c -n2 , will need to run /sbin/gabconfig -c -x if only one system comes up and both systems were down.

Cluster conf: /etc/VRTSvcs/conf/config/main.cf
Has exact details on what the cluster contains.

Most executables are in: /opt/VRTSvcs/bin or /sbin

Changing Configurations

ALWAYS be very careful when changing the cluster configurations. The only time I needed to change the cluster configuration was when Vipul upgraded Oracle versions and ORACLE_HOME changed directories. This is a very dangerous thing to do.

There are two ways of changing the configurations. The method one uses if the system is up (cluster is running on at least one node, preferably on both):

haconf -makerw
run needed commands (ie. hasys ....)
haconf -dump -makero

If both systems are down:

hastop -all (shouldn't need this as cluster is down)
cp main.cf main.cf.save
vi main.cf
hacf -verify /etc/VRTSvcs/conf/config
hacf -generate /etc/VRTSvcs/conf/config
hastart

An excellent reference book for Veritas Clusters is:

• Shared Data Clusters: Scaleable, Manageable, and Highly Available Systems (VERITAS Series) - this will provide you with the background knowledge of how clusters work, how to get the best performance from your cluster, and more.