Oracle RAC/ASM Interview Questions & Answers

Question 1. What Is The Main Purpose Of Oracle Real Application Clusters (rac)?

Answer :

• Oracle Real Application (RAC) provides the interaction of executable file with the Oracle database.
• It allows the running of any packaged or custom built application with the Oracle database that is running on a server pool.
• It provides very high level of availability, flexibility and scalability to run the application and store it to the database.
• It creates the database such that if the pool fails then the database is continued to run from the remaining servers and the load can be distributed.
• It makes it easier for the administrator to maintain many servers at the same time by load-balancing techniques and providing provision to add more and more servers when the load increases.

Question 2. Where Are The Clusterware Files Stored On A Rac Environment?

Answer :

The Clusterware is installed on each node (on an Oracle Home) and on the shared disks (the voting disks and the CSR file).

Question 3. What Is Scan?

Answer :

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.

Question 4. What Is Required By Oracle Rac Database To Connect To A Network?

Answer :

• Oracle RAC requires an active connection of the network to the LAN (Local Area Network) so that the database server can be found and connected.
• The database server is further having connections with application servers that store the applications and allow user to transfer their data.
• The connection is required with the server pool so that the transfer of services and applications can be done on demand basis.
• The interconnection between the networks is really important as it has to maintain the overall flow of the pools and the resources.
• Oracle RAC provides support to redundant interconnects relatively and it provides an overall infrastructure solution.
• The load balancing and inter-node messaging can be handled more carefully when the networks or the servers are interconnected to each other.

Question 5. How Is Possible To Install A Rac If We Don’t Have A Cfs?

Answer :

This is possible by using a raw device.

Question 6. What Are The Types Of Connection Load-balancing?

Answer :

There are two types of connection load-balancing: server-side load balancing and client-side load balancing.

Question 7. What Are The Provisions And Resources Provided In The Oracle’s Cloud Server?

Answer :

• Oracle’s cloud server provides scalability by adding more servers to a pool when there is a requirement of any processing power or space.
• Provision to pay per hour/use as per the requirement, to, keep the overall cost low and build the functionality on the high-end systems.
• Oracle RAC provides the platform’s architecture as it provides low-cost hardware platform to deliver high quality service and provide more scalability and availability.
• This reduces the administration cost and provides good management techniques and tools to monitor the services.
• This allows the users to build their own infrastructure on the basis of cloud.

Question 8. Where Are The Database Software Files Stored On A Rac Environment?

Answer :

The base software is installed on each node of the cluster and the database storage on the shared disks.

Question 9. What Is Grd?

Answer :

GRD stands for Global Resource Directory. The GES and GCS maintain records of the status of each datafile and each cached block using global resource directory. This process is referred to as cache fusion and helps in data integrity.

Question 10. Explain The Hardware Architecture Used In Oracle Rac?

Answer :

• The Hardware Architecture of the Oracle RAC clusters provides a shared architecture with the server pools and allows all the storage devices to be shared.
• Hardware Architecture supports different types of storage networks like Network attached storage (NAS), Storage Area Network (SAN) and SCSI disks.
• Hardware architecture is such that it provides appropriate choices for the storage pools and system that provides scalability and flexibility to the overall system.
• The architecture should contain the input and output for the application that need to be developed and then the system can have more scalability.
• Hardware architecture supports more application to be added in the server pool and allows better integration of services.

Question 11. Do You Know Another Cluster Vendor?

Answer :

HP Tru64 Unix, Veritas, Microsoft

Question 12. What Are The Performance Views In An Oracle Rac Environment?

Answer :

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.

Question 13. What Is The Function Of Cache Fusion In Oracle Rac?

Answer :

• Cache function is used to show the storage of the information in the clustered network with the Oracle database.
• This uses the database transfer medium and it involves two nodes where one reads the data block from the disk and another write the data to the same disk.
• It provides very good performance and increases the flexibility in terms of execution of the application that is using the platform.
• RAC uses a dedicated server for its network connection and the cache fusion is an internal part to the cluster.
• It uses the same database and keeps the things in the cache till the information is not needed anymore by any other application. It queries the data only when it totally necessary to do it.
• The query from the user always results in the most current version even after the data is being modified.

Question 14. What Kind Of Storage We Can Use For The Rac Database Storage?

Answer :

• OCFS (Release 1 or 2)
• ASM
• raw devices
• third party cluster file system such as GPFS or Veritas

Question 15. What Is A Crs Resource?

Answer :

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.

Question 16. How Is Clustered Database Important In Oracle Rac Architecture?

Answer :

• Clustered database is just like a single database accessed by multiple instances that are running on the server.
• The instances are being run separately or individually on the server pool and when the demands rise they are shifted to acquire more space according to the requirements.
• Clustered database provides dynamic access to the database and on the demand of additional resources they are added to the server pool.
• If one cluster is taking up the load then that load is shared between other clusters running on the server and the application services are provided in a much faster and better way.
• This also allows the adding of additional resources dynamically to the server pool with no downtime and the application starts running soon it is deployed on the server.

Question 17. What Is An Ocfs2?

Answer :

The OCFS2 is the Oracle (version 2) Cluster File System which can be used for the Oracle Real Application Cluster.

Question 18. How Do We Remove Asm From An Oracle Rac Environment?

Answer :

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

Question 19. Describe The Oracle Real Application Clusters Architecture?

Answer :

• Oracle RAC consists of a database that is represented in a clustered manner in the architecture.
• The cluster is the collection or pool of independent servers that make up one single system.
• Cluster architecture provides more flexibility to manage and follow a modular incremental approach to improve the fault errors and provide an incremental system.
• This architecture provides the maximum security in terms of ensuring high availability of the resources to the users.
• It provides the resources on demand and provides hardware architecture such that a single point of failure is being removed.
• The architecture provides the decoupling of the Oracle instance like the process and memory that are running on the server from the Oracle database.

Question 20. What Is A Cfs?

Answer :

A cluster File System (CFS) is a file system that may be accessed (read and write) by all members in a cluster at the same time. This implies that all members of a cluster have the same view.

Question 21. What Is The Use Of Ocr?

Answer :

Oracle Clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR (Oracle Cluster Registry).

Question 22. What Are The Key Components Of Oracle’s Maximum Availability Architecture?

Answer :

• Oracle Real Application Clusters are the key components of the existing architecture.
• It provides directions and management of the applications that needs to be architect using the architecture.
• It provides high scalability of the applications that is being run on a single server and it takes the advantage of lower cost commodity hardware to reduce the cost.
• It enables the Oracle database to be run and maintained using the business application that are on the server pools and involves packaged products as well.
• It provides a way to integrate the in-house applications that are developed using the oracle database and its technology.
• It allows easy management of the server by providing the ability to remove the server as a single point of failure in the database application environment.

Question 23. What Kind Of Storage We Can Use For The Shared Clusterware Files?

Answer :

• OCFS (Release 1 or 2)
• raw devices
• third party cluster file system such as GPFS or Veritas

Question 24. How Does An Oracle Clusterware Manage Crs Resources?

Answer :

Oracle Clusterware manages CRS resources based on the configuration information of CRS resources stored in OCR (Oracle Cluster Registry).

Question 25. What Is Asm?

Answer :

               In Oracle Database 10g/11g there are two types of instances: database and ASM instances. The ASM instance, which is generally named +ASM, is started with the INSTANCE_TYPE=ASM init.ora parameter. This parameter, when set, signals the Oracle initialization routine to start an ASM instance and not a standard database instance. Unlike the standard database instance, the ASM instance contains no physical files; such as logfiles, controlfiles or datafiles, and only requires a few init.ora parameters for startup.
               Upon startup, an ASM instance will spawn all the basic background processes, plus some new ones that are specific to the operation of ASM. The STARTUP clauses for ASM instances are similar to those for database instances. For example, RESTRICT prevents database instances from connecting to this ASM instance. NOMOUNT starts up an ASM instance without mounting any disk group. MOUNT option simply mounts all defined diskgroups
              For RAC configurations, the ASM SID is +ASMx instance, where x represents the instance number.

Question 26. What Are The Key Benefits Of Asm?

Answer :

ASM provides filesystem and volume manager capabilities built into the Oracle database kernel. Withthis capability, ASM simplifies storage management tasks, such as creating/laying out databases and disk space management. Since ASM allows disk management to be done using familiar create/alter/drop SQL statements, DBAs do not need to learn a new skill set or make crucial decisions on provisioning.
The following are some key benefits of ASM:

• ASM spreads I/O evenly across all available disk drives to prevent hot spots and maximize performance.
• ASM eliminates the need for over provisioning and maximizes storage resource utilization facilitating database consolidation.
• Inherent large file support.
• Performs automatic online redistribution after the incremental addition or removal of storage  capacity.
• Maintains redundant copies of data to provide high availability, or leverages 3rd party RAID functionality.
• Supports Oracle Database as well as Oracle Real Application Clusters (RAC).
• Capable of leveraging 3rd party multipathing technologies.
• For simplicity and easier migration to ASM, an Oracle database can contain ASM and non-ASM files.
• Any new files can be created as ASM files whilst existing files can also be migrated to ASM.
• RMAN commands enable non-ASM managed files to be relocated to an ASM disk group.
• Enterprise Manager Database Control or Grid Control can be used to manage ASM disk and file activities.

Question 27. How Does Database Connects To Asm Instance?

Answer :

The database communicates with ASM instance using the ASMB (umblicus process) process. Once the database obtains the necessary extents from extent map, all database IO going  forward is processed through by the database processes, bypassing ASM. Thus we say ASM is not really in the IO path. So, the question how do we make ASM go faster…..you don’t have to.

Question 28. What Init.ora Parameters Does A User Need To Configure For Asm Instances?

Answer :

The default parameter settings work perfectly for ASM. The only parameters needed for 11g ASM:

• PROCESSES*
• ASM_DISKSTRING*
• ASM_DISKGROUPS
• INSTANCE_TYPE

Question 29. How Does The Database Interact With The Asm Instance And How Do I Make Asm Go Faster?

Answer :

ASM is not in the I/O path so ASM does not impede the database file access. Since the RDBMS instance is performing raw I/O, the I/O is as fast as possible.

Question 30. Do I Need To Define The Rdbms Filesystemio_options Parameter When I Use Asm?

Answer :

No. The RDBMS does I/O directly to the raw disk devices, the FILESYSTEMIO_OPTIONS  parameter is only for filesystems.

Question 31. Why Oracle Recommends Two Disk Groups?

Answer :

Oracle recommends two diskgroups to provide a balance of manageability, utilization, and performance.

Question 32. We Have A 16 Tb Database. I’m Curious About The Number Of Disk Groups We Should Use; E.g. 1 Large Disk Group, A Couple Of Disk Groups, Or Otherwise?

Answer :

For VLDBs you will probably end up with different storage tiers; e.g with some of our large customers they have Tier1 (RAID10 FC), Tier2 (RAID5 FC), Tier3 (SATA), etc. Each one of these is mapped to a diskgroup.

Question 33. We Have A New App And Don’t Know Our Access Pattern, But Assuming Mostly Sequential Access, What Size Would Be A Good Au Fit?

Answer :

For 11g ASM/RDBMS it is recommended to use 4MB ASM AU for disk groups. See Metalink Note 810484.1

Question 34. Would It Be Better To Use Bigfile Tablespaces, Or Standard Tablespaces For Asm?

Answer :

The use of Bigfile tablespaces has no bearing on ASM (or vice versa). In fact most database object related decisions are transparent to ASM.

Question 35. What Is The Best Lun Size For Asm?

Answer :

There is no best size! In most cases the storage team will dictate to you based on their standardized LUN size. The ASM administrator merely has to communicate the ASM Best Practices and application  characteristics to storage folks :
• Need equally sized / performance LUNs
• Minimum of 4 LUNs
• The capacity requirement
• The workload characteristic (random r/w, sequential r/w) & any response time SLA
Using this info , and their standards, the storage folks should build a nice LUN group set for you.

Question 36. In 11g Rac We Want To Separate Asm Admins From Dbas And Create Different Users And Groups. How Do We Set This Up?

Answer :

For clarification
• Separate Oracle Home for ASM and RDBMS.
• RDBMS instance connects to ASM using OSDBA group of the ASM instance.
Thus, software owner for each RDBMS instance connecting to ASM must be a member of ASM's OSDBA group.
• Choose a different OSDBA group for ASM instance (asmdba) than for RDBMS instance (dba)
• In 11g, ASM administrator has to be member of a separate SYSASM group to separate ASM Admin and DBAs.

Question 37. Can My Rdbms And Asm Instances Run Different Versions?

Answer :

Yes. ASM can be at a higher version or at lower version than its client databases. There’s two:
components of compatiblity: Software compatibility
Diskgroup compatibility attributes: compatible.asm, compatible.rdbms.

Question 38. Where Do I Run My Database Listener From; I.e., Asm Home Or Db Home?

Answer :

It is recommended to run the listener from the ASM HOME. This is particularly important for RAC env, since the listener is a node-level resource. In this config, you can create additional [user] listeners from the database homes as needed.

Question 39. How Do I Backup My Asm Instance?

Answer :

Not applicable! ASM has no files to backup, as its does not contain controlfile,redo logs etc.

Question 40. When Should I Use Rman And When Should I Use Asmcmd Copy?

Answer :

RMAN is the recommended and most complete and flexible method to backup and transport database files in ASM.
ASMCMD copy is good for copying single files
• Supports all Oracle file types
• Can be used to instantiate a Data Guard environment
• Does not update the controlfile
• Does not create OMF files

Question 41. I'm Going To Do Add Disks To My Asm Diskgroup, How Long Will This Rebalance Take?

Answer :

Rebalance time is heavily driven by the three items:
1) Amount of data currently in the diskgroup
2) IO bandwidth available on the server
3) ASM_POWER_LIMIT or Rebalance Power Level

Question 42. We Are Migrating To A New Storage Array. How Do I Move My Asm Database From Storage A To Storage B?

Answer :

Given that the new and old storage are both visible to ASM, simply add the new disks to the ASM disk group and drop the old disks. ASM rebalance will migrate data online.

Question 43. Is It Possible To Unplug An Asm Disk Group From One Platform And Plug Into A Server On Another Platform (for Example, From Solaris To Linux)?

Answer :

No. Cross-platform disk group migration not supported. To move datafiles between endian-ness platforms, you need to use XTTS, Datapump or Streams.

Question 44. How Does Asm Work With Multipathing Software?

Answer :

It works great! Multipathing software is at a layer lower than ASM, and thus is transparent.
You may need to adjust ASM_DISKSTRING to specify only the path to the multipathing pseudo devices.

Question 45. Is Asm Constantly Rebalancing To Manage “hot Spots”?

Answer :

No.ASM provides even distribution of extents across all disks in a disk group. Since each disk will equal number of extents, no single disk will be hotter than another. Thus the answer NO, ASM does not dynamically move hot spots, because hot spots simply do not occur in ASM configurations. Rebalance only occurs on storage configuration changes (e.g. add, drop, or resize disks).

Question 46. What Are The File Types That Asm Support And Keep In Disk Groups?

Answer :

• Control files
• Flashback logs
• Data Pump dump sets

• Data files
• DB SPFILE
• Data Guard configuration

• Temporary data files
• RMAN backup sets
• Change tracking bitmaps

• Online redo logs
• RMAN data file copies
• OCR files

• Archive logs
• Transport data files
• ASM SPFILE

Question 47. List Key Benefits Of Asm?

Answer :

• Stripes files rather than logical volumes
• Provides redundancy on a file basis
• Enables online disk reconfiguration and dynamic rebalancing
• Reduces the time significantly to resynchronize a transient failure by tracking changes while disk is offline
• Provides adjustable rebalancing speed
• Is cluster-aware
• Supports reading from mirrored copy instead of primary copy for extended clusters
• Is automatically installed as part of the Grid Infrastructure

Question 48. What Is Asm Striping?

Answer :

ASM can use variable size data extents to support larger files, reduce memory requirements, and improve performance.
Each data extent resides on an individual disk.
Data extents consist of one or more allocation units.
The data extent size is:

• Equal to AU for the first 20,000 extents (0–19999)
• Equal to 4 × AU for the next 20,000 extents (20000–39999)
• Equal to 16 × AU for extents above 40,000

ASM stripes files using extents with a coarse method for load balancing or a fine method to reduce latency.

• Coarse-grained striping is always equal to the effective AU size.
• Fine-grained striping is always equal to 128 KB.

Question 49. How Many Asm Diskgroups Can Be Created Under One Asm Instance?

Answer :

ASM imposes the following limits:

• 63 disk groups in a storage system
• 10,000 ASM disks in a storage system
• Two-terabyte maximum storage for each ASM disk (non-Exadata)
• Four-petabyte maximum storage for each ASM disk (Exadata)
• 40-exabyte maximum storage for each storage system
• 1 million files for each disk group
• ASM file size limits (database limit is 128 TB):

1. External redundancy maximum file size is 140 PB.
2. Normal redundancy maximum file size is 42 PB.
3. High redundancy maximum file size is 15 PB.

Question 50. What Is A Diskgroup?

Answer :

A disk group consists of multiple disks and is the fundamental object that ASM manages. Each disk group contains the metadata that is required for the management of space in the disk group. The ASM instance manages the metadata about the files in a Disk Group in the same way that a file system manages metadata about its files. However, the vast majority of I/O operations do not pass through the ASM instance. In a moment we will look at how file I/O works with respect to the ASM instance.