What command would you use to check the availability of the RAC system?
crs_stat -t -v (-t -v are optional)
How do we verify that RAC instances are running?
SQL>select * from V$ACTIVE_INSTANCES;
The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.
What are Oracle Clusterware Components ?
Voting Disk — Oracle RAC
uses the voting disk to manage cluster membership by way of a health
check and arbitrates cluster ownership among the instances in case of
network failures. The voting disk must reside on shared disk.
Oracle Cluster Registry (OCR)
— Maintains cluster configuration information as well as configuration
information about any cluster database within the cluster. The OCR must
reside on shared disk that is accessible by all of the nodes in your
cluster
How do you backup the OCR ?
There is an automatic backup mechanism for OCR. The default location is : $ORA_CRS_HOME\cdata\"clustername"\
To display backups :
#ocrconfig -showbackup
To restore a backup :
#ocrconfig -restore
With Oracle RAC 10g Release 2 or later, you can also use the export command:
#ocrconfig -export -s online, and use -import option to restore the contents back.
With Oracle RAC 11g Release 1, you can do a manaual backup of the OCR with the command:
# ocrconfig -manualbackup
How do you backup voting disk ?
#dd if=voting_disk_name of=backup_file_name
How do I identify the voting disk location ?
#crsctl query css votedisk
How do I identify the OCR file location ?
check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform)
or
#ocrcheck
Is ssh required for normal Oracle RAC operation ?
"ssh" are not required for normal Oracle RAC operation. However "ssh"
should be enabled for Oracle RAC and patchset installation.
What is SCAN?
Single Client Access Name (SCAN) is s a new Oracle Real Application
Clusters (RAC) 11g Release 2 feature that provides a single name for
clients to access an Oracle Database running in a cluster. The benefit
is clients using SCAN do not need to change if you add or remove nodes
in the cluster.
Click here for more details from Oracle
What is the purpose of Private Interconnect ?
Clusterware uses the private interconnect for cluster synchronization
(network heartbeat) and daemon communication between the the clustered
nodes. This communication is based on the TCP protocol.RAC uses the interconnect for cache fusion (UDP) and inter-process
communication (TCP). Cache Fusion is the remote memory mapping of Oracle
buffers, shared between the caches of participating nodes in the
cluster.
Why do we have a Virtual IP (VIP) in Oracle RAC?
Without
using VIPs or FAN, clients connected to a node that died will often
wait for a TCP timeout period (which can be up to 10 min) before getting
an error. As a result, you don't really have a good HA solution without
using VIPs.
When
a node fails, the VIP associated with it is automatically failed over
to some other node and new node re-arps the world indicating a new MAC
address for the IP. Subsequent packets sent to the VIP go to the new
node, which will send error RST packets back to the clients. This
results in the clients getting errors immediately.
How many nodes are supported in a RAC Database?
10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.
What is voting disk?
Voting Disk is a file that sits in the shared storage area and must be
accessible by all nodes in the cluster. All nodes in the cluster
registers their heart-beat information in the voting disk, so as to
confirm that they are all operational. If heart-beat information of any
node in the voting disk is not available that node will be evicted from
the cluster. The CSS (Cluster Synchronization Service) daemon in the
clusterware maintains the heart beat of all nodes to the voting disk.
When any node is not able to send heartbeat to voting disk, then it will
reboot itself, thus help avoiding the split-brain syndrome.
For high availability, Oracle recommends that you have a minimum of three or odd number (3 or greater) of votingdisks.
Voting Disk – is file that resides on shared storage and Manages
cluster members. Voting disk reassigns cluster ownership between the
nodes in case of failure.
The Voting Disk Files are used by Oracle Clusterware to determine
which nodes are currently members of the cluster. The voting disk files
are also used in concert with other Cluster components such as CRS to
maintain the clusters integrity.
Oracle Database 11g Release 2 provides the ability to store the
voting disks in ASM along with the OCR. Oracle Clusterware can access
the OCR and the voting disks present in ASM even if the ASM instance is
down. As a result CSS can continue to maintain the Oracle cluster even
if the ASM instance has failed.
How many voting disks are you maintaining ?
By default Oracle will create 3 voting disk files in ASM.
Oracle expects that you will configure at least 3 voting disks for
redundancy purposes. You should always configure an odd number of voting
disks >= 3. This is because loss of more than half your voting disks
will cause the entire cluster to fail.
You should plan on allocating 280MB for each voting disk file. For
example, if you are using ASM and external redundancy then you will need
to allocate 280MB of disk for the voting disk. If you are using ASM and
normal redundancy you will need 560MB.
Why we need to keep odd number of voting disks ?
Oracle expects that you will configure at least 3 voting disks for
redundancy purposes. You should always configure an odd number of voting
disks >= 3. This is because loss of more than half your voting disks
will cause the entire cluster to fail.
What is SCAN? (11gR2 feature)
Single Client Access Name (SCAN) eliminates the need to change
TNSNAMES entry when nodes are added to or removed from the Cluster. RAC
instances register to SCAN listeners as remote listeners. Oracle
recommends assigning 3 addresses to SCAN, which will create 3 SCAN
listeners, though the cluster has got dozens of nodes.. SCAN is a domain
name registered to at least one and up to three IP addresses, either in
DNS (Domain Name Service) or GNS (Grid Naming Service). The SCAN must
resolve to at least one address on the public network. For high
availability and scalability, Oracle recommends configuring the SCAN to
resolve to three addresses.
What are SCAN components in a cluster?
1.SCAN Name
2.SCAN IPs (3)
3.SCAN Listeners (3)
What are the requirements for Oracle Clusterware?
1. External Shared Disk to store Oracle Cluster ware file (Voting Disk and Oracle Cluster Registry – OCR)
2. Two netwrok cards on each cluster ware node (and three set of IP address) -
Network Card 1 (with IP address set 1) for public network
Network Card 2 (with IP address set 2) for private network (for inter
node communication between rac nodes used by clusterware and rac
database)
IP address set 3 for Virtual IP (VIP) (used as Virtual IP address for client connection and for connection failover)
3. Storage Option for OCR and Voting Disk – RAW, OCFS2 (Oracle Cluster File System), NFS, …..
How to find location of OCR file when CRS is down?
If you need to find the location of OCR (Oracle Cluster Registry) but your CRS is down.
When the CRS is down:
Look into “ocr.loc” file, location of this file changes depending on the OS:
On Linux: /etc/oracle/ocr.loc
On Solaris: /var/opt/oracle/ocr.loc
When CRS is UP:
Set ASM environment or CRS environment then run the below command:
ocrcheck
In 2 node RAC, how many NIC’s are r using ?
2 network cards on each clusterware node
Network Card 1 (with IP address set 1) for public network
Network Card 2 (with IP address set 2) for private network (for inter
node communication between rac nodes used by clusterware and rac
database)
In 2 node RAC, how many IP’s are r using ?
6 – 3 set of IP address
## eth1-Public: 2
## eth0-Private: 2
## VIP: 2
How to find IP’s information in RAC ?
Edit the /etc/hosts file as shown below:
# Do not remove the following line, or various programs
# that requires network functionality will fail.
127.0.0.1 localhost.localdomain localhost
## Public Node names
192.168.10.11 node1-pub.hingu.net node1-pub
192.168.10.22 node2-pub.hingu.net node2-pub
## Private Network (Interconnect)
192.168.0.11 node1-prv node1-prv
192.168.0.22 node2-prv node2-prv
## Private Network (Network Area storage)
192.168.1.11 node1-nas node1-nas
192.168.1.22 node2-nas node2-nas
192.168.1.33 nas-server nas-server
## Virtual IPs
192.168.10.111 node1-vip.hingu.net node1-vip
192.168.10.222 node2-vip.hingu.net node2-vip
What is difference between RAC ip addresses ?
Public IP adress is the normal IP address typically used by DBA and SA
to manage storage, system and database. Public IP addresses are reserved
for the Internet.
Private IP address is used only for internal clustering processing
(Cache Fusion) (aka as interconnect). Private IP addresses are reserved
for private networks.
VIP is used by database applications to enable fail over when one
cluster node fails. The purpose for having VIP is so client connection
can be failover to surviving nodes in case there is failure
Can application developer access the private ip ?
No. private IP address is used only for internal clustering processing (Cache Fusion) (aka as interconnect)
How many OCR and voting
disks should one have?
For redundancy, one should
have at least two OCR disks and three voting disks (raw disk partitions).
These disk partitions should
be spread across different physical disks.
Why we required to maintain
odd number of voting disks?
Odd number of disk are to
avoid split brain,When Nodes in cluster can't
talk to each other they run to lock the Voting disk and whoever lock the more
disk will survive,if disk number are even there
are chances that node might lock 50% of disk (2 out of 4) then how to decide
which node to evict.whereas when number is odd,
one will be higher than other and each for cluster to evict the node with less
number.
How you check the health of
Your RAC Database?
'crsctl' command from root or oracle user can
be used to check the clusterware health But for starting or stopping we have to
use root user or any privilege user.
[oracle@TEST_NODE1 ~]$ crsctl
check crs
CSS appears healthy
CRS appears healthy
EVM appears healthy
How you will backup your
RAC Database?
Backup strategy of RAC Database:An RAC Database consists of
1)OCR
2)Voting disk
3)Database files,
controlfiles, redolog files & Archive log files
Give the usage of srvctl ?
srvctl start instance -d
db_name -i "inst_name_list" [-o start_options]
srvctl stop instance -d name
-i "inst_name_list" [-o stop_options]
srvctl stop instance -d orcl
-i "orcl3,orcl4" -o immediate
srvctl start database -d name
[-o start_options]
srvctl stop database -d name
[-o stop_options]
srvctl start database -d orcl
-o mount
What are the major RAC wait
events?
In a RAC environment the
buffer cache is global across all instances in the cluster and hence the
processing differs.
The most common wait events
related to this are gc cr request
and gc buffer busy
GC CR request :the time it
takes to retrieve the data from the remote cache
Reason: RAC Traffic Using
Slow Connection or Inefficient queries (poorly tuned queries will increase the
amount of data blocks requested by an Oracle session.
The more blocks requested
typically means the more often a block will need to be read from a remote
instance via the interconnect.)
GC BUFFER BUSY: It is the
time the remote instance locally spends accessing the requested data block.
How do we verify an
existing current backup of OCR?
We can verify the current
backup of OCR using the following command : ocrconfig -showbackup
How to move OCR and Voting
disk to new storage device? ( verify in non-prod first)
Moving OCR
==========
You must be logged in as the
root user, because root owns the OCR files.
Also an ocrmirror must be in place before
trying to replace the OCR device.
Make sure there is a recent
backup of the OCR file before making any changes:
ocrconfig –showbackup
If there is not a recent
backup copy of the OCR file, an export can be taken for the current OCR file.
Use the following command to generate an export of the online OCR file:
In 10.2
# ocrconfig –export -s online
In 11g
# ocrconfig -manualbackup
The new OCR disk must be
owned by root, must be in the oinstall group, and must have permissions set to
640. Provide at least 100 MB disk space for the OCR.
On one node as root run:
# ocrconfig -replace ocr
# ocrconfig -replace
ocrmirror
Now run ocrcheck to verify if
the OCR is pointing to the new file
Moving Voting Disk
==================
Note: crsctl votedisk
commands must be run as root
Shutdown the Oracle
Clusterware (crsctl stop crs as root) on all nodes before making any
modification to the voting disk. Determine the current voting disk location
using:
crsctl query css votedisk
Take a backup of all voting
disk:
dd if=voting_disk_name
of=backup_file_name
To move a Voting Disk,
provide the full path including file name:
crsctl delete css votedisk
–force
crsctl add css votedisk
–force
After modifying the voting
disk, start the Oracle Clusterware stack on all nodes
# crsctl start crs
Verify the voting disk
location using
crsctl query css votedisk
What is split brain ?
In RAC environment, server
nodes communicate with each other using High speed private interconnects network. A split brain
situation happens when all the links of the private interconnect fail to
respond to each other but instances are
still up and running. So each instance thinks that the other nodes/instances
are dead and that it should take
over the ownership.
In split brain situation,
instances independtly access the data and modify the same blocks and the
database will end up with changed
database overwritten which could lead to data corruption. To avoid this,
various algorithm are implemented to
handle split brain scenario.
In RAC, the IMR (Instance
Membership Recovery) service is one of the one of the efficient algorithm used to detect & resolve
the split-brain syndrome. When one instance fails to communicate with other instances or when one
instance becomes inactive due to any reason and is unable to issue the control
file heartbeat, the split brain is
detected and the detecting instance will evict the failed instance from the database.This process is
called node eviction.
What is FAN?
Applications can use Fast
Application Notification (FAN) to enable rapid failure detection, balancing of
connection pools after failures, and re-balancing of
connection pools when failed components are repaired.The FAN process uses system
events that Oracle publishes when cluster servers become unreachable or if
network interfaces fail.
What is FCF?
Fast Connection Failover
provides high availability to FAN integrated clients, such as clients that use
JDBC, OCI, or ODP.NET. If you configure the client
to use fast connection failover, then the client automatically subscribes to
FAN events and can react to database UP and DOWN events.
In response, Oracle gives the
client a connection to an active instance that provides the requested database
service.
What
is the difference between CRSCTL and SRVCTL?
crsctl
manages clusterware-related operations:
· Starting and stopping Oracle Clusterware
· Enabling and disabling Oracle Clusterware daemons
· Registering cluster resources
srvctl
manages Oracle resource–related operations:
· Starting and stopping database instances and services
· Also from 11gR2 manages the cluster resources like
network,vip,disks etc
How to
control Oracle Clusterware?
To
start or stop Oracle Clusterware on a specific node:
#
crsctl stop crs
#
crsctl start crs
To
enable or disable Oracle Clusterware on a specific node:
#
crsctl enable crs
#
crsctl disable crs
How to
check the cluster (all nodes) status?
To
check the viability of Cluster Synchronization Services (CSS) across nodes:
$
crsctl check cluster
CRS-4537:
Cluster Ready Services is online
CRS-4529:
Cluster Synchronization Services is online
CRS-4533:
Event Manager is online
How to
check the cluster (one node) status?
$
crsctl check crs
CRS-4638:
Oracle High Availability Services is online
CRS-4537:
Cluster Ready Services is online
CRS-4529:
Cluster Synchronization Services is online
CRS-4533:
Event Manager is online
How do you troubleshoot node reboot ?
Please check metalink ...
Note 265769.1 Troubleshooting CRS Reboots
Note.559365.1 Using Diagwait as a diagnostic to get more information for diagnosing Oracle Clusterware Node evictions.
