1. What is the use of ASM (or) Why ASM preferred over filesystem?
Answer:
ASM provides striping and mirroring.
a) Provides automatic load balancing over all the available disks, thus reducing hot spots in the file system.
b) Prevents fragmentation of disks, so you don’t need to manually relocate data to tune I/O performance.
c) Adding disks is straight forward – ASM automatically performs online disk reorganization when you add or remove storage.
d) Uses redundancy features available in intelligent storage arrays.
e)The storage system can store all types of database files.
f) Using disk group makes configuration easier, as files are placed into disk groups.
2. What are the init parameters related to ASM?
Answer:
INSTANCE_TYPE = ASM
ASM_POWER_LIMIT = 11
ASM_DISKSTRING = '/dev/rdsk/*s2', '/dev/rdsk/c1*'
ASM_DISKGROUPS = DG_DATA, DG_FRA
3. What is rebalancing (or) what is the use of ASM_POWER_LIMIT?
Answer:
ASM_POWER_LIMIT is dynamic parameter, which will be useful for rebalancing the data across disks.
Value can be 1(lowest) to 11 (highest).
4. What are different types of redundancies in ASM & explain?
Answer:
Normal redundancy - for 2-way mirroring, requiring two failure groups, when ASM allocates an extent for a normal redundancy file, ASM allocates a primary copy and a secondary copy. ASM chooses the disk on which to store the secondary copy in a different failure group other than the primary copy.
High redundancy - for 3-way mirroring, requiring three failure groups, in this case the extent is mirrored across 3 disks.
External redundancy - to not use ASM mirroring. This is used if you are using hardware mirroring or third party redundancy mechanism like RAID, Storage arrays.
5. When you will use external redundancy and what are the advantages of it?
6. How to copy file to/from ASM from/to filesystem?
Answer:
By using ASMCMD cp command
7. How to find out the databases, which are using the ASM instance?
Answer:
ASMCMD> lsct
SQL> select DB_NAME from V$ASM_CLIENT;
8. What are different types of stripings in ASM & their differences?
Answer:
Fine-grained striping
Coarse-grained striping
9. What happen if you miss "+" sign while adding datafile in ASM disk group ?
10. What is allocation unit and what is default value of au_size and how to change?
Answer:
Every ASM disk is divided into allocation units (AU). An AU is the fundamental unit of allocation within a disk group. A file extent consists of one or more AU. An ASM file consists of one or more file extents.
CREATE DISKGROUP disk_group_2 EXTERNAL REDUNDANCY DISK '/dev/sde1' ATRRIBUTE 'au_size' = '32M';
lsdg
select NAME,ALLOCATION_UNIT_SIZE from v$asm_diskgroup;
11. What are the background processes in ASM?
Answer:
ASMB - This ASMB process is used to provide information to and from cluster synchronization services used by ASM to manage the disk resources. It's also used to update statistics and provide a heart beat mechanism.
RBAL, Re-Balance - RBAL is the ASM related process that performs rebalancing of disk resources controlled by ASM.
ARBx, Actual Rebalance - ARBx is configured by ASM_POWER_LIMIT, a slave for rebalancing operations.
12. What processes does the rebalancing?
Answer:
RBAL, ARBx
13. How to dismount ASM disk group from particular instance in RAC?
14. How to add/remove disk to/from diskgroup?
Answer:
ALTER DISKGROUP data1 ADD DISK '/devices/diska5';
ALTER DISKGROUP disk_group_1 DROP DISK diska2;
Oracle RAC Interview Questions And Answers
Q1) What are the differences between Oracle RAC and Oracle Grid ?
Oracle RAC Vs Oracle Grid
RAC GRID
Single system image avaiable No single system image
Proprietary interoperability with VIA No standards available
Single ownership Multiple Ownerships
Disciverable membership services Central Index and decentral information to discover
Moderate throughput Either too high or too low throughput
Guarantees capacity High capacty, varies sometimes
Most number of commodity computers Commodity and High-end computers
Centralised user management Distributed user management
Centralised resource management Distributed resource management
Central allocation and scheduling DecentraliDistributed allocation and scheduling
Q1) What is cache fusion?
Ans. In a RAC environment, it is the combining of data blocks, which are shipped across the interconnect from remote database caches (SGA) to the local node, in order to fulfill the requirements for a transaction (DML, Query of Data Dictionary).
Q2) What is split brain?
Ans. When database nodes in a cluster are unable to communicate with each other, they may continue to process and modify the data blocks independently. If the
same block is modified by more than one instance, synchronization/locking of the data blocks does not take place and blocks may be overwritten by others in the cluster. This state is called split brain.
Q3) What is the difference between Crash recovery and Instance recovery?
Ans. When an instance crashes in a single node database on startup a crash recovery takes place. In a RAC enviornment the same recovery for an instance is performed by the surviving nodes called Instance recovery.
Q4) What is the interconnect used for?
Ans. It is a private network which is used to ship data blocks from one instance to another for cache fusion. The physical data blocks as well as data dictionary blocks are shared across this interconnect.
Q5) How do you determine what protocol is being used for Interconnect traffic?
Ans. One of the ways is to look at the database alert log for the time period when the database was started up.
Q6) What methods are available to keep the time synchronized on all nodes in the cluster?
Ans. Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.
Q7) What files components in RAC must reside on shared storage?
Ans. Spfiles, ControlFiles, Datafiles and Redolog files should be created on shared storage.
Q8) Where does the Clusterware write when there is a network or Storage missed heartbeat?
Ans. The network ping failure is written in $CRS_HOME/log
Q9) How do you find out what OCR backups are available?
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Ans. The ocrconfig -showbackup can be run to find out the automatic and manually run backups.
Q10) If your OCR is corrupted what options do have to resolve this?
Ans. You can use either the logical or the physical OCR backup copy to restore the Repository.
Q11) How do you find out what object has its blocks being shipped across the instance the most?
Ans. You can use the dba_hist_seg_stats.
Q12) What is a VIP in RAC use for?
Ans. The VIP is an alternate Virtual IP address assigned to each node in a cluster. During a node failure the VIP of the failed node moves to the surviving node and relays to the application that the node has gone down. Without VIP, the application will wait for TCP timeout and then find out that the session is no longer live due to the failure.
Q13) How do we know which database instances are part of a RAC cluster?
Ans. You can query the V$ACTIVE_INSTANCES view to determine the member instances of the RAC cluster.
Q14) What is OCLUMON used for in a cluster environment?
Ans. The Cluster Health Monitor (CHM) stores operating system metrics in the CHM repository for all nodes in a RAC cluster. It stores information on CPU, memory, process, network and other OS data, This information can later be retrieved and used to troubleshoot and identify any cluster related issues. It is a default component of the 11gr2 grid install. The data is stored in the master repository and replicated to a standby repository on a different node.
Q15) What would be the possible performance impact in a cluster if a less powerful node (e.g. slower CPU’s) is added to the cluster?
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Ans. All processing will show down to the CPU speed of the slowest server.
Q16) What is the purpose of OLR?
Ans. Oracle Local repository contains information that allows the cluster processes to be started up with the OCR being in the ASM storage ssytem. Since the ASM file system is unavailable until the Grid processes are started up a local copy of the contents of the OCR is required which is stored in the OLR.
Q17) What is the default memory allocation for ASM?
Ans. In 10g the default SGA size is 1G in 11g it is set to 256M and in 12c ASM it is set back to 1G.
Q18) How do you backup ASM Metadata?
Ans. You can use md_backup to restore the ASM diskgroup configuration in-case of ASM diskgroup storage loss.
Q19) What files can be stored in the ASM diskgroup?
Ans. In 11g the following files can be stored in ASM diskgroups.
Datafiles
Redo logfiles
Spfiles
In 12c the files below can also new be stored in the ASM Diskgroup
Password file
Q20) What it the ASM POWER_LIMIT?
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Ans. This is the parameter which controls the number of Allocation units the ASM instance will try to rebalance at any given time. In ASM versions less than 11.2.0.3 the default value is 11 however it has been changed to unlimited in later versions.
Q21) What is a rolling upgrade?
Ans. A patch is considered a rolling if it is can be applied to the cluster binaries without having to shutting down the database in a RAC environment. All nodes in the cluster are patched in a rolling manner, one by one, with only the node which is being patched unavailable while all other instance open.
Q22) What are some of the RAC specific parameters?
Ans. Some of the RAC parameters are:
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
INSTANCE_TYPE (RDBMS or ASM)
ACTIVE_INSTANCE_COUNT
UNDO_MANAGEMENT
Q23) What is the future of the Oracle Grid?
Ans. The Grid software is becoming more and more capable of not just supporting HA for Oracle Databases but also other applications including Oracle’s applications. With 12c there are more features and functionality built-in and it is easier to deploy these pre-built solutions, available for common Oracle applications.
Q24) What components of the Grid should I back up?
Ans. The backups should include OLR, OCR and ASM Metadata.
Q25) Is there an easy way to verify the inventory for all remote nodes
Ans. You can run the OPATCH LSINVENTORY -ALL_NODES command from a single node to look at the inventory details for all nodes in the cluster.
SCANs uses IP's not assigned to any interface. Clusterware will be in charge of it. It will direct the requests to the appropriate servers in the cluster. VIPs are the IPs which also CRS maintains for each node. They must do this so that failover is possible, in the case one node fails it can fail over the VIP to another node.
The main purpose of SCAN is to provide ease of management/connection. For instance you can add new nodes to the cluster without changing your client TNSnames. This is because Oracle will automatically distribute requests accordingly based on the SCAN IPs which point to the underlying VIPs. Scan listeners do the bridge between clients and the underlying local listeners which are VIP-dependent.
Answer:
ASM provides striping and mirroring.
a) Provides automatic load balancing over all the available disks, thus reducing hot spots in the file system.
b) Prevents fragmentation of disks, so you don’t need to manually relocate data to tune I/O performance.
c) Adding disks is straight forward – ASM automatically performs online disk reorganization when you add or remove storage.
d) Uses redundancy features available in intelligent storage arrays.
e)The storage system can store all types of database files.
f) Using disk group makes configuration easier, as files are placed into disk groups.
2. What are the init parameters related to ASM?
Answer:
INSTANCE_TYPE = ASM
ASM_POWER_LIMIT = 11
ASM_DISKSTRING = '/dev/rdsk/*s2', '/dev/rdsk/c1*'
ASM_DISKGROUPS = DG_DATA, DG_FRA
3. What is rebalancing (or) what is the use of ASM_POWER_LIMIT?
Answer:
ASM_POWER_LIMIT is dynamic parameter, which will be useful for rebalancing the data across disks.
Value can be 1(lowest) to 11 (highest).
4. What are different types of redundancies in ASM & explain?
Answer:
Normal redundancy - for 2-way mirroring, requiring two failure groups, when ASM allocates an extent for a normal redundancy file, ASM allocates a primary copy and a secondary copy. ASM chooses the disk on which to store the secondary copy in a different failure group other than the primary copy.
High redundancy - for 3-way mirroring, requiring three failure groups, in this case the extent is mirrored across 3 disks.
External redundancy - to not use ASM mirroring. This is used if you are using hardware mirroring or third party redundancy mechanism like RAID, Storage arrays.
5. When you will use external redundancy and what are the advantages of it?
6. How to copy file to/from ASM from/to filesystem?
Answer:
By using ASMCMD cp command
7. How to find out the databases, which are using the ASM instance?
Answer:
ASMCMD> lsct
SQL> select DB_NAME from V$ASM_CLIENT;
8. What are different types of stripings in ASM & their differences?
Answer:
Fine-grained striping
Coarse-grained striping
9. What happen if you miss "+" sign while adding datafile in ASM disk group ?
10. What is allocation unit and what is default value of au_size and how to change?
Answer:
Every ASM disk is divided into allocation units (AU). An AU is the fundamental unit of allocation within a disk group. A file extent consists of one or more AU. An ASM file consists of one or more file extents.
CREATE DISKGROUP disk_group_2 EXTERNAL REDUNDANCY DISK '/dev/sde1' ATRRIBUTE 'au_size' = '32M';
lsdg
select NAME,ALLOCATION_UNIT_SIZE from v$asm_diskgroup;
11. What are the background processes in ASM?
Answer:
ASMB - This ASMB process is used to provide information to and from cluster synchronization services used by ASM to manage the disk resources. It's also used to update statistics and provide a heart beat mechanism.
RBAL, Re-Balance - RBAL is the ASM related process that performs rebalancing of disk resources controlled by ASM.
ARBx, Actual Rebalance - ARBx is configured by ASM_POWER_LIMIT, a slave for rebalancing operations.
12. What processes does the rebalancing?
Answer:
RBAL, ARBx
13. How to dismount ASM disk group from particular instance in RAC?
14. How to add/remove disk to/from diskgroup?
Answer:
ALTER DISKGROUP data1 ADD DISK '/devices/diska5';
ALTER DISKGROUP disk_group_1 DROP DISK diska2;
Oracle RAC Interview Questions And Answers
Q1) What are the differences between Oracle RAC and Oracle Grid ?
Oracle RAC Vs Oracle Grid
RAC GRID
Single system image avaiable No single system image
Proprietary interoperability with VIA No standards available
Single ownership Multiple Ownerships
Disciverable membership services Central Index and decentral information to discover
Moderate throughput Either too high or too low throughput
Guarantees capacity High capacty, varies sometimes
Most number of commodity computers Commodity and High-end computers
Centralised user management Distributed user management
Centralised resource management Distributed resource management
Central allocation and scheduling DecentraliDistributed allocation and scheduling
Q1) What is cache fusion?
Ans. In a RAC environment, it is the combining of data blocks, which are shipped across the interconnect from remote database caches (SGA) to the local node, in order to fulfill the requirements for a transaction (DML, Query of Data Dictionary).
Q2) What is split brain?
Ans. When database nodes in a cluster are unable to communicate with each other, they may continue to process and modify the data blocks independently. If the
same block is modified by more than one instance, synchronization/locking of the data blocks does not take place and blocks may be overwritten by others in the cluster. This state is called split brain.
Q3) What is the difference between Crash recovery and Instance recovery?
Ans. When an instance crashes in a single node database on startup a crash recovery takes place. In a RAC enviornment the same recovery for an instance is performed by the surviving nodes called Instance recovery.
Q4) What is the interconnect used for?
Ans. It is a private network which is used to ship data blocks from one instance to another for cache fusion. The physical data blocks as well as data dictionary blocks are shared across this interconnect.
Q5) How do you determine what protocol is being used for Interconnect traffic?
Ans. One of the ways is to look at the database alert log for the time period when the database was started up.
Q6) What methods are available to keep the time synchronized on all nodes in the cluster?
Ans. Either the Network Time Protocol(NTP) can be configured or in 11gr2, Cluster Time Synchronization Service (CTSS) can be used.
Q7) What files components in RAC must reside on shared storage?
Ans. Spfiles, ControlFiles, Datafiles and Redolog files should be created on shared storage.
Q8) Where does the Clusterware write when there is a network or Storage missed heartbeat?
Ans. The network ping failure is written in $CRS_HOME/log
Q9) How do you find out what OCR backups are available?
Subscribe to our youtube channel to get new updates..!
Ans. The ocrconfig -showbackup can be run to find out the automatic and manually run backups.
Q10) If your OCR is corrupted what options do have to resolve this?
Ans. You can use either the logical or the physical OCR backup copy to restore the Repository.
Q11) How do you find out what object has its blocks being shipped across the instance the most?
Ans. You can use the dba_hist_seg_stats.
Q12) What is a VIP in RAC use for?
Ans. The VIP is an alternate Virtual IP address assigned to each node in a cluster. During a node failure the VIP of the failed node moves to the surviving node and relays to the application that the node has gone down. Without VIP, the application will wait for TCP timeout and then find out that the session is no longer live due to the failure.
Q13) How do we know which database instances are part of a RAC cluster?
Ans. You can query the V$ACTIVE_INSTANCES view to determine the member instances of the RAC cluster.
Q14) What is OCLUMON used for in a cluster environment?
Ans. The Cluster Health Monitor (CHM) stores operating system metrics in the CHM repository for all nodes in a RAC cluster. It stores information on CPU, memory, process, network and other OS data, This information can later be retrieved and used to troubleshoot and identify any cluster related issues. It is a default component of the 11gr2 grid install. The data is stored in the master repository and replicated to a standby repository on a different node.
Q15) What would be the possible performance impact in a cluster if a less powerful node (e.g. slower CPU’s) is added to the cluster?
Oracle RAC Certification Training!
Explore Curriculum
Ans. All processing will show down to the CPU speed of the slowest server.
Q16) What is the purpose of OLR?
Ans. Oracle Local repository contains information that allows the cluster processes to be started up with the OCR being in the ASM storage ssytem. Since the ASM file system is unavailable until the Grid processes are started up a local copy of the contents of the OCR is required which is stored in the OLR.
Q17) What is the default memory allocation for ASM?
Ans. In 10g the default SGA size is 1G in 11g it is set to 256M and in 12c ASM it is set back to 1G.
Q18) How do you backup ASM Metadata?
Ans. You can use md_backup to restore the ASM diskgroup configuration in-case of ASM diskgroup storage loss.
Q19) What files can be stored in the ASM diskgroup?
Ans. In 11g the following files can be stored in ASM diskgroups.
Datafiles
Redo logfiles
Spfiles
In 12c the files below can also new be stored in the ASM Diskgroup
Password file
Q20) What it the ASM POWER_LIMIT?
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21
NOV
Thursday
6:30 AM IST
24
NOV
Sunday
6:30 AM IST
28
NOV
Thursday
6:30 AM IST
01
DEC
Sunday
7:00 AM IST
More Batches
Ans. This is the parameter which controls the number of Allocation units the ASM instance will try to rebalance at any given time. In ASM versions less than 11.2.0.3 the default value is 11 however it has been changed to unlimited in later versions.
Q21) What is a rolling upgrade?
Ans. A patch is considered a rolling if it is can be applied to the cluster binaries without having to shutting down the database in a RAC environment. All nodes in the cluster are patched in a rolling manner, one by one, with only the node which is being patched unavailable while all other instance open.
Q22) What are some of the RAC specific parameters?
Ans. Some of the RAC parameters are:
CLUSTER_DATABASE
CLUSTER_DATABASE_INSTANCE
INSTANCE_TYPE (RDBMS or ASM)
ACTIVE_INSTANCE_COUNT
UNDO_MANAGEMENT
Q23) What is the future of the Oracle Grid?
Ans. The Grid software is becoming more and more capable of not just supporting HA for Oracle Databases but also other applications including Oracle’s applications. With 12c there are more features and functionality built-in and it is easier to deploy these pre-built solutions, available for common Oracle applications.
Q24) What components of the Grid should I back up?
Ans. The backups should include OLR, OCR and ASM Metadata.
Q25) Is there an easy way to verify the inventory for all remote nodes
Ans. You can run the OPATCH LSINVENTORY -ALL_NODES command from a single node to look at the inventory details for all nodes in the cluster.
SCANs uses IP's not assigned to any interface. Clusterware will be in charge of it. It will direct the requests to the appropriate servers in the cluster. VIPs are the IPs which also CRS maintains for each node. They must do this so that failover is possible, in the case one node fails it can fail over the VIP to another node.
The main purpose of SCAN is to provide ease of management/connection. For instance you can add new nodes to the cluster without changing your client TNSnames. This is because Oracle will automatically distribute requests accordingly based on the SCAN IPs which point to the underlying VIPs. Scan listeners do the bridge between clients and the underlying local listeners which are VIP-dependent.
Note:If original author needs credit for this,Please email me the information,Will give credit
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