Q 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.
Q what is dynamic remastering ? When will the dynamic remastering happens?
dynamic remastering is ability to move the ownership of resource from one instance to another instance in RAC. dynamic resource remastering is used to implement for resource affinity for increased performance. resource affinity optimized the system in situation where update transactions are being executed in one instance. when activity shift to another instance the resource affinity correspondingly move to another instance. If activity is not localized then resource ownership is hashed to the instance.
In 10g dynamic remastering happens in file+object level.the process of remastering is very stringent. For one instance should touch more than 50 times than the other instance in particular period(say 10 mints). this touch ratio and time can be tuned by gc_affinity_limit and _gc_affinity_time parameter.
Q 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
Q 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
Q How you check the services in RAC Node?
We can check the service or start the services with 'srvctl' command.load balanced/TAF service named RAC online.
[oracle@TEST_NODE1 ~]$ srvctl start service -d orcl -s RAC [oracle@TEST_NODE1 ~]$ crsstat
Q If there is some issue with virtual IP how will you troubleshoot it?How will you change virtual ip?
To change the VIP (virtual IP) on a RAC node, use the command
[oracle@testnode oracle]$ srvctl modify nodeapps -A new_address
Backup strategy of RAC Database:
An RAC Database consists of 1)OCR 2)Voting disk & 3)Database files, controlfiles, redolog files & Archive log files
Q Do you have any idea of load balancing in application?How load balancing is done?
Q What is RAC?
RAC stands for Real Application cluster. It is a clustering solution from Oracle Corporation that ensures high availability of databases by providing instance failover, media failover features.
RAC stands for Real Application Cluster, you have n number of instances running in their own separate nodes and based on the shared storage. Cluster is the key component and is a collection of servers operations as one unit. RAC is the best solution for high performance and high availably. Non RAC databases has single point of failure in case of hardware failure or server crash.
Q 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
Q Mention the Oracle RAC software components ?
Oracle RAC is composed of two or more database instances. They are composed of Memory structures and background processes same as the single instance database.Oracle RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache Service) that enable cache fusion.Oracle RAC instances are composed of following background processes:
ACMS—Atomic Controlfile to Memory Service (ACMS)
GTX0-j—Global Transaction Process LMON—Global Enqueue Service Monitor LMD—Global Enqueue Service Daemon LMS—Global Cache Service Process LCK0—Instance Enqueue Process RMSn—Oracle RAC Management Processes (RMSn) RSMN—Remote Slave Monitor
Q What is GRD?
GRD stands for Global Resource Directory. The GES and GCS maintains records of the statuses of each datafile and each cahed block using global resource directory.This process is referred to as cache fusion and helps in data integrity.
Q What are the different network components are in 10g RAC?
public, private, and vip components
Private interfaces is for intra node communication. VIP is all about availability of application. When a node fails then the VIP component fail over to some other node, this is the reason that all applications should based on vip components means tns entries should have vip entry in the host list
Q Give Details on ACMS:
ACMS stands for Atomic Controlfile Memory Service.In an Oracle RAC environment ACMS is an agent that ensures a distributed SGA memory update(ie)SGA updates are globally committed on success or globally aborted in event of a failure.
Q 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.
The process provides transparent support for XA global transactions in a RAC environment.The database autotunes the number of these processes based on the workload of XA global transactions.
This process monitors global enques and resources across the cluster and performs global enqueue recovery operations.This is called as Global Enqueue Service Monitor.
This process is called as global enqueue service daemon. This process manages incoming remote resource requests within each instance.
This process is called as Global Cache service process.This process maintains statuses of datafiles and each cahed block by recording information in a Global Resource Dectory(GRD).This process also controls the flow of messages to remote instances and manages global data block access and transmits block images between the buffer caches of different instances.This processing is a part of cache fusion feature.
This process is called as Instance enqueue process.This process manages non-cache fusion resource requests such as libry and row cache requests.
This process is called as Oracle RAC management process.These pocesses perform managability tasks for Oracle RAC.Tasks include creation of resources related Oracle RAC when new instances are added to the cluster.
Below script generate svrctl add script for database, instance, service and 11G listeners from OCR from current RAC.
Save the result of the script and run it at new RAC. for DBNAME in $(srvctl config database) do # Generate DB resource srvctl config database -d $DBNAME -a | awk -v dbname="$DBNAME" \ 'BEGIN { FS=":" } $1~/Oracle home/ || $1~/ORACLE_HOME/ {dbhome = "-o" $2} $1~/Spfile/ || $1~/SPFILE/ {spfile = "-p" $2} $1~/Disk Groups/ {dg = "-a" $2} END { if (avail == "-a ") {avail = ""}; printf "%s %s %s %s %s\n", "srvctl add database -d ", dbname, dbhome, spfile, dg }' # Generate Instance resource srvctl status database -d $DBNAME | awk -v dbname="$DBNAME" \ '$4~/running/ { printf "%s %s %s %s %s %s\n", "srvctl add instance -d ",dbname, " -i ", $2 ," -n ", $7 } $5~/running/ { printf "%s %s %s %s %s %s \n", "srvctl add instance -d ",dbname, " -i ", $2 ," -n ", $8 }' # Modify instance for 10G - ASM dependency if [ $(echo $ORACLE_HOME | grep "1020" | wc -l ) -eq 1 ] then srvctl status database -d $DBNAME | awk -v dbname="$DBNAME" \ '$2~/1$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -s +ASM1" } $2~/2$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -s +ASM2" } $2~/3$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -s +ASM3" } $2~/4$/ { printf "%s %s %s %s %s \n", "srvctl modify instance -d ",dbname, " -i ", $2 ," -s +ASM4" }' fi echo "srvctl start database -d $DBNAME" # Generate Service resource snamelist=$(srvctl status service -d $DBNAME | awk '{print $2}') for sname in $snamelist do srvctl config service -d $DBNAME -s $sname| awk -v dbname="$DBNAME" -v sname=$sname \ 'BEGIN { FS=":"} $1~/Preferred instances/ {pref = "-r" $2} $1~/PREF/ {pref = "-r" $2; sub(/AVAIL/, "", pref) } $1~/Available instances/ {avail = "-a" $2} $2~/AVAIL/ {avail = "-a" $3} $1~/Failover type/ {ft = "-e" $2} $1~/Failover method/ {fm = "-m" $2} $1~/Runtime Load Balancing Goal/ {g = "-B" $2} END { if (avail == "-a ") {avail = ""}; printf "%s %s %s %s %s %s %s %s %s %s\n", "srvctl add service -d ",dbname, "-s ", sname, pref, avail ,ft, fm,g, "-P BASIC"}' echo "srvctl start service -d $DBNAME -s $sname" done done # Listener at 11G Home. 10G listener can't ba added with srvctl. srvctl config listener | awk \ 'BEGIN { FS=":"; state = 0; } $1~/Name/ {lname = "-l" $2; state=1}; $1~/Home/ && state == 1 {ohome = "-o" $2; state=2;} $1~/End points/ && state == 2 {lport = "-p " $3; state=3;} state == 3 {if (ohome != "-o ") {printf "%s %s %s %s\n", "srvctl add listener ", lname, ohome, lport;} state=0;}'
Q Give details on RSMN
This process is called as Remote Slave Monitor.This process manages background slave process creation andd communication on remote instances. This is a background slave process.This process performs tasks on behalf of a co-ordinating process running in another instance.
Q What components in RAC must reside in shared storage?
All datafiles, controlfiles, SPFIles, redo log files must reside on cluster-aware shred storage.
Q What is the significance of using cluster-aware shared storage in an Oracle RAC environment?
All instances of an Oracle RAC can access all the datafiles,control files, SPFILE's, redolog files when these files are hosted out of cluster-aware shared storage which are group of shared disks.
ASM(automatic storage management),raw disk devices,network file system(NFS), OCFS2 and OCFS(Oracle Cluster Fie systems).
An interconnect network is a private network that connects all of the servers in a cluster. The interconnect network uses a switch/multiple switches that only the nodes in the cluster can access.
Q How can we configure the cluster interconnect?
Configure User Datagram Protocol(UDP) on Gigabit ethernet for cluster interconnect.On unix and linux systems we use UDP and RDS(Reliable data socket) protocols to be used by Oracle Clusterware.Windows clusters use the TCP protocol.
No, crossover cables are not supported with Oracle Clusterware intercnects.
Cluster interconnect is used by the Cache fusion for inter instance communication.
Users can access a RAC database using a client/server configuration or through one or more middle tiers ,with or without connection pooling.Users can use oracle services feature to connect to database.
Applications should use the services feature to connect to the Oracle database.Services enable us to define rules and characteristics to control how users and applications connect to database instances.
The charateristics include a unique name, workload balancing and failover options,and high availability characteristics.
Oracle Net Services enable the load balancing of application connections across all of the instances in an Oracle RAC database.
A virtl IP address or VIP is an alternate IP address that the client connectins use instead of the standard public IP address. To configureVIP address, we need to reserve a spare IP address for each node, and the IP addresses must use the same subnet as the public network.
If a node fails, then the node's VIP address fails over to another node on which the VIP address can accept TCP connections but it cannot accept Oracle connections.
VIP addresses failover happens when the node on which the VIP address runs fails, all interfaces for the VIP address fails, all interfaces for the VIP address are disconnected from the network.
When a VIP address failover happens, Clients that attempt to connect to the VIP address receive a rapid connection refused error .They don't have to wait for TCP connection timeout messages.
Oracle RAC cluster can be administered as a single image using OEM(Enterprise Manager),SQL*PLUS,Servercontrol(SRVCTL),clusterverificationutility(cvu),DBCA,NETCA
Issue the following query from any one node connecting through SQL*PLUS.
$connect sys/sys as sysdba SQL>select * from V$ACTIVE_INSTANCES; The query gives the instance number under INST_NUMBER column,host_:instancename under INST_NAME column.
Q What is FAN?
Fast application Notification as it abbreviates to FAN relates to the events related to instances,services and nodes.This is a notification mechanism that Oracle RAc uses to notify other processes about the configuration and service level information that includes service status changes such as,UP or DOWN events.Applications can respond to FAN events and take immediate action.
Q Where can we apply FAN UP and DOWN events?
FAN UP and FAN DOWN events can be applied to instances,services and nodes.
State the use of FAN events in case of a cluster configuration change? During times of cluster configuration changes,Oracle RAC high availability framework publishes a FAN event immediately when a state change occurs in the cluster.So applications can receive FAN events and react immediately.This prevents applications from polling database and detecting a problem after such a state change.
Q Why should we have seperate homes for ASm instance?
It is a good practice to have ASM home seperate from the database hom(ORACLE_HOME).This helps in upgrading and patching ASM and the Oracle database software independent of each other.Also,we can deinstall the Oracle database software independent of the ASM instance.
Q What is the advantage of using ASM?
Having ASM is the Oracle recommended storage option for RAC databases as the ASM maximizes performance by managing the storage configuration across the disks.ASM does this by distributing the database file across all of the available storage within our cluster database environment.
It is a new ASM feature from Database 11g.ASM instances in Oracle database 11g release(from 11.1) can be upgraded or patched using rolling upgrade feature. This enables us to patch or upgrade ASM nodes in a clustered environment without affecting database availability.During a rolling upgrade we can maintain a functional cluster while one or more of the nodes in the cluster are running in different software versions.
No,it can be used only for Oracle database 11g releases(from 11.1).
Q State the initialization parameters that must have same value for every instance in an Oracle RAC database
Some initialization parameters are critical at the database creation time and must have same values.Their value must be specified in SPFILE or PFILE for every instance.The list of parameters that must be identical on every instance are given below:
ACTIVE_INSTANCE_COUNT ARCHIVE_LAG_TARGET COMPATIBLE CLUSTER_DATABASE CLUSTER_DATABASE_INSTANCE CONTROL_FILES DB_BLOCK_SIZE DB_DOMAIN DB_FILES DB_NAME DB_RECOVERY_FILE_DEST DB_RECOVERY_FILE_DEST_SIZE DB_UNIQUE_NAME INSTANCE_TYPE (RDBMS or ASM) PARALLEL_MAX_SERVERS REMOTE_LOGIN_passWORD_FILE UNDO_MANAGEMENT
Q What is ORA-00603: ORACLE server session terminated by fatal error or ORA-29702: error occurred in Cluster Group Service operation?
RAC node name was listed in the loopback address...
These parameters can be identical on all instances only if these parameter values are set to zero.
What two parameters must be set at the time of starting up an ASM instance in a RAC environment?The parameters CLUSTER_DATABASE and INSTANCE_TYPE must be set.
Oracle clusterware is made up of components like voting disk and Oracle Cluster Registry(OCR).
Oracle clusterware is used to manage high-availability operations in a cluster.Anything that Oracle Clusterware manages is known as a CRS resource.Some examples of CRS resources are database,an instance,a service,a listener,a VIP address,an application process etc.
Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).
Oracle clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR(Oracle Cluster Registry).
OIFCFG - allocating and deallocating network interfaces
OCRCONFIG - Command-line tool for managing Oracle Cluster Registry OCRDUMP - Identify the interconnect being used CVU - Cluster verification utility to get status of CRS resources
We can delete instances using silent mode or interactive mode using DBCA(Database Configuration Assistant).
We need to stop and delete the instance in the node first in interactive or silent mode.After that asm can be removed using srvctl tool as follows:
srvctl stop asm -n node_name srvctl remove asm -n node_name We can verify if ASM has been removed by issuing the following command: srvctl config asm -n node_name
Issue the following srvctl command:
srvctl config database -d database_name cd CRS_HOME/bin ./crs_stat
We can verify the current backup of OCR using the following command : ocrconfig -showbackup
What are the performance views in an Oracle RAC environment? We have v$ views that are instance specific. In addition we have GV$ views called as global views that has an INST_ID column of numeric data type.GV$ views obtain information from individual V$ views. What are the types of connection load-balancing? There are two types of connection load-balancing:server-side load balancing and client-side load balancing.
Client-side balancing happens at client side where load balancing is done using listener.In case of server-side load balancing listener uses a load-balancing advisory to redirect connections to the instance providing best service.
The three main benefits are availability, scalability, and the ability to use low cost commodity hardware. RAC allows an application to scale vertically, by adding CPU, disk and memory resources to an individual server. But RAC also provides horizontal scalability, which is achieved by adding new nodes into the cluster. RAC also allows an organization to bring these resources online as they are needed. This can save a small or midsize organization a lot of money in the early stages of a project.
In a RAC environment, if a node in the cluster fails, the application continues to run on the surviving nodes contained in the cluster. If your application is configured correctly, most users won't even know that the node they were running on became unavailable.
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.
We have public, private, and VIP components. Private interfaces is for intra node communication. VIP is all about availability of application. When a node fails then the VIP component will fail over to some other node, this is the reason that all applications should be based on VIP components. This means that tns entries should have VIP entry in the host list.
PROD1 PROD2 PROD3
CPU 8 CPU 15 CPU 8 32 GB RAM 12 GB RAM 16 GB RAM
What are you looking for here? What tuning information do you expect?
It is a 3 node cluster with different hardware configuration running RAC. I would put 20% of the memory for Oracle in each node. So that would mean that the SGA is different in each of the nodes. Also since the CPU's are different PROD2 can have more number of max number of processes as compared to the rest of them. But as I said this is just configuration, this is not tuning. Question is not clear.
Q Write a sample script for RMAN for the recovery if all the instance are down.(First explain the procedure how you will restore)
Bring all nodes down.
Start one Node Restore all datafiles and archive logs. Recover 1 Node. Open the database. bring other nodes up. Confirm that all nodes are operational.
Clients are performing some operation and suddenly one of the datafile is experiencing problem what do you do? The cluster is a two node one.
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
With Oracle Clusterware 11g release 2, Oracle Universal Installer (OUI) detects when the minimum requirements for an installation are not met, and creates shell scripts, called fixup scripts, to finish incomplete system configuration steps. If OUI detects an incomplete task, then it generates fixup scripts (runfixup.sh). You can run the fixup script after you click the Fix and Check Again Button.
The Fixup script does the following:
■ If necessary sets kernel parameters to values required for successful installation,
including:
– Shared memory parameters.
– Open file descriptor and UDP send/receive parameters.
■ Sets permissions on the Oracle Inventory (central inventory) directory.
■ Reconfigures primary and secondary group memberships for the installation
owner, if necessary, for the Oracle Inventory directory and the operating system
privileges groups.
■ Sets shell limits if necessary to required values.
After fulfilling the pre-installation requirements, the basic installation steps to follow are: 1. Invoke the Oracle Universal Installer (OUI) 2. Enter the different information for some components like: - name of the cluster - public and private node names - location for OCR and Voting Disks - network interfaces used for RAC instances -etc. 3. After the Summary screen, OUI will start copying under the $CRS_HOME (this is the $ORACLE_HOME for Oracle Clusterware) in the local node the libraries and executables. - here we will have the daemons and scripts init.* created and configured properly. Oracle Clusterware is formed of several daemons, each one of which have a special function inside the stack. Daemons are executed via the init.* scripts (init.cssd, init.crsd and init.evmd). - note that for CRS only some client libraries are recreated, but not all the executables (as for the RDBMS). 4. Later the software is propagated to the rest of the nodes in the cluster and the oraInventory is updated. 5. The installer will ask to execute root.sh on each node. Until this step the software for Oracle Clusterware is inside the $CRS_HOME. Running root.sh will create several components outside the $CRS_HOME: - OCR and VD will be formated. - control files (or SCLS_SRC files ) will be created with the correct contents to start Oracle Clusterware. These files are used to control some aspects of Oracle Clusterware like: - enable/disable processes from the CSSD family (Eg. oprocd, oslsvmon) - stop the daemons (ocssd.bin, crsd.bin, etc). - prevent Oracle Clusterware from being started when the machine boots. - etc. - /etc/inittab will be updated and the init process is notified. In order to start the Oracle Clusterware daemons, the init.* scripts first need to be run. These scripts are executed by the daemon init. To accomplish this some entries must be created in the file /etc/inittab. - the different processes init.* (init.cssd, init.crsd, etc) will start the daemons (ocssd.bin, crsd.bin, etc). When all the daemons are running then we can say that the installation was successful - On 10.2 and later, running root.sh on the last node in the cluster also will create the nodeapps (VIP, GSD and ONS). On 10.1, VIPCA is executed as part of the RAC installation. 6. After running root.sh on each node, we need to continue with the OUI session. After pressing the 'OK' button OUI will include the information for the public and cluster_interconnect interfaces. Also CVU (Cluster Verification Utility) will be executed. Cluster Synchronization Services (ocssd) — Manages cluster node membership and runs as the oracle user; failure of this process results in cluster restart. Cluster Ready Services (crsd) — The crs process manages cluster resources (which could be a database, an instance, a service, a Listener, a virtual IP (VIP) address, an application process, and so on) based on the resource's configuration information that is stored in the OCR. This includes start, stop, monitor and failover operations. This process runs as the root user Event manager daemon (evmd) —A background process that publishes events that crs creates. Process Monitor Daemon (OPROCD) —This process monitor the cluster and provide I/O fencing. OPROCD performs its check, stops running, and if the wake up is beyond the expected time, then OPROCD resets the processor and reboots the node. An OPROCD failure results in Oracle Clusterware restarting the node. OPROCD uses the hangcheck timer on Linux platforms. RACG (racgmain, racgimon) —Extends clusterware to support Oracle-specific requirements and complex resources. Runs server callout scripts when FAN events occur. •LMS—Global Cache Service Process •LMD—Global Enqueue Service Daemon •LMON—Global Enqueue Service Monitor •LCK0—Instance Enqueue Process To ensure that each Oracle RAC database instance obtains the block that it needs to satisfy a query or transaction, Oracle RAC instances use two processes, the Global Cache Service (GCS) and the Global Enqueue Service (GES). The GCS and GES maintain records of the statuses of each data file and each cached block using a Global Resource Directory (GRD). The GRD contents are distributed across all of the active instances.
Q 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
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.
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
#dd if=voting_disk_name of=backup_file_name
#crsctl query css votedisk
check /var/opt/oracle/ocr.loc or /etc/ocr.loc ( depends upon platform) or #ocrcheck "ssh" are not required for normal Oracle RAC operation. However "ssh" should be enabled for Oracle RAC and patchset installation.
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.
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.
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
This is most likely due to a fault in interconnect network.
Check netstat -s if you see "fragments dropped" or "packet reassemblies failed" , Work with your system administrator find the fault with network.
10g Release 2, support 100 nodes in a cluster using Oracle Clusterware, and 100 instances in a RAC database.
Q Srvctl cannot start instance, I get the following error PRKP-1001 CRS-0215, however sqlplus can start it on both nodes? How do you identify the problem?
Set the environmental variable SRVM_TRACE to true.. And start the instance with srvctl. Now you will get detailed error stack.
The Oracle Notification Service (ONS) daemon is an daemon started by the CRS clusterware as part of the nodeapps. There is one ons daemon started per clustered node.
The Oracle Notification Service daemon receive a subset of published clusterware events via the local evmd and racgimon clusterware daemons and forward those events to application subscribers and to the local listeners. This in order to facilitate: a. the FAN or Fast Application Notification feature or allowing applications to respond to database state changes. b. the 10gR2 Load Balancing Advisory, the feature that permit load balancing accross different rac nodes dependent of the load on the different nodes. The rdbms MMON is creating an advisory for distribution of work every 30seconds and forward it via racgimon and ONS to listeners and applications.
Users can access a RAC database using a client/server configuration or through one or more middle tiers, with or without connection pooling. Users can use oracle services feature to connect to database.
Applications should use the services feature to connect to the Oracle database. Services enable us to define rules and characteristics to control how users and applications connect to database instances.
The characteristics include a unique name, workload balancing and failover options, and high availability characteristics.
A voting disk is a file that manages information about node membership.
Following administrative tasks are performed with the voting disk :
1) Backing up voting disks
2) Recovering Voting disks
3) Adding voting disks
4) Deleting voting disks
5) Moving voting disks
1) Oracle recommends that you back up your voting disk after the initial cluster creation and after we complete any node addition or deletion procedures.
2) First, as root user, stop Oracle Clusterware (with the crsctl stop crs command) on all nodes. Then, determine the current voting disk by issuing the following command:
crsctl query votedisk css
3) Then, issue the dd or ocopy command to back up a voting disk, as appropriate.
Give the syntax of backing up voting disks:-
On Linux or UNIX systems:
dd if=voting_disk_name of=backup_file_name
where,
voting_disk_name is the name of the active voting disk
backup_file_name is the name of the file to which we want to back up the voting disk contents
On Windows systems, use the ocopy command:
ocopy voting_disk_name backup_file_name
Oracle recommends us to use the dd command to backup the voting disk with a minimum block size of 4KB.
To restore the backup of your voting disk, issue the dd or ocopy command for Linux and UNIX systems or ocopy for Windows systems respectively.
On Linux or UNIX systems:
dd if=backup_file_name of=voting_disk_name
On Windows systems, use the ocopy command:
ocopy backup_file_name voting_disk_name
where,
backup_file_name is the name of the voting disk backup file
voting_disk_name is the name of the active voting disk
Q How can we add and remove multiple voting disks?
If we have multiple voting disks, then we can remove the voting disks and add them back into our environment using the following commands, where path is the complete path of the location where the voting disk resides:
crsctl delete css votedisk path
crsctl add css votedisk path
Before making any modification to the voting disk, as root user, stop Oracle Clusterware using the crsctl stop crs command on all nodes.
To add a voting disk, issue the following command as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to add:
crsctl add css votedisk path -force
To move a voting disk, issue the following commands as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to move:
crsctl delete css votedisk path -force
crsctl add css votedisk path -force
To remove a voting disk, issue the following command as the root user, replacing the path variable with the fully qualified path name for the voting disk we want to remove:
crsctl delete css votedisk path -force
After modifying the voting disk, restart Oracle Clusterware using the crsctl start crs command on all nodes, and verify the voting disk location using the following command:
crsctl query css votedisk
If our cluster is down, then we can include the -force option to modify the voting disk configuration, without interacting with active Oracle Clusterware daemons. However, using the -force option while any cluster node is active may corrupt our configuration.
Ref: https://www.linkedin.com/pulse/racasmvoting-disk-interview-questions-answer-amr-hassan?trk=v-feed |
Wednesday, August 30, 2017
RAC/ASM/VOTING DISK Interview Questions & Answer
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