BRIEF SUMMARY OF SCAN
SCAN is required for
oracle 11gR2 GRID INFRASTRUCTURE installation and OUI
can’t complete unless SCAN is defined.
In TYPICAL installation , the
SCAN name you provide is also the name of the cluster and this name must be
globally unique throughout your enterprise.
The SCAN is the address used by all clients connecting to
the cluster. The SCAN name is a domain name registered to three IP addresses
either in the DNS or Grid Naming Service (GNS).
The SCAN address must be on the same subnet as the VIP
address for nodes in the cluster.
To use DNS method for SCAN,
Network administrator must create a single name that resolves to 3 separate IP
addresses. Use nslookup at least twice or thrice to see
the round–robin algorithm work.
For GNS to operate, only 1
static address is required to be registered in the DNS i.e for the GNS vip .
The node VIP and 3 SCAN VIP’s are obtained from DHCP server
when using GNS.
Without setting up a DNS based SCAN resolution , you can use
a HOSTS – FILE based workaround. In this case, you
would use a typical host file entry to resolve the SCAN to only 1 ip address.
If hosts file is used to
resolve SCAN hostname, you will receive CVU failure at the end of
installation. (NOTE : 887471.1)
For each of the 3 IP addresses that the SCAN resolves to , a
SCAN VIP resource is created and a SCAN LISTENER is created .
Sample TNS entry for SCAN :
ORCL =
(DESCRIPTION =
(ADDRESS =
(PROTOCOL = TCP)(HOST = racnode-scan.india.com)(PORT = 1521))
(CONNECT_DATA =
(SERVER =
DEDICATED)
(SERVICE_NAME =
ORCL.INDIA.COM)
)
)
Sample TNS entry without SCAN :
ORCL =
(DESCRIPTION=
(ADDRESS_LIST=
(ADDRESS=(PROTOCOL=tcp)(HOST=racnode1-vip.india.com)(PORT=1521))
(ADDRESS=(PROTOCOL=tcp)(HOST=racnode2-vip.india.com)(PORT=1521))
)
(CONNECT_DATA=(SERVICE_NAME=ORCL.INDIA.COM))
)
The database registers with the SCAN listener through the remote_listener parameter in the init.ora/spfile .
SCAN automatically provides both FAILOVER and LOAD BALANCING . Each SCAN listener keeps updated cluster
load statistics.
In order to make the
cluster aware of the modified SCAN
configuration, delete the entry in the hosts-file and then issue : “srvctl
modify scan –n <scan-name>” as the root user on one node in the cluster .
SEE MY NEXT POST
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