Are you preparing for Automatic Storage Management (ASM) interview? ASM is the feature of Oracle. Customers are provided with simple storage management of log files, control files, database files which is same in all platforms and servers. The data is stored as Disk Groups (referred as collection of groups)using ASM. There can be many disk groups to allocate storage. ASM automates the data to be placed in those disk groups automatically. Many of the people are not aware of this job so there is huge demand for this technology in the market. Good knowledge on these concepts will fetch you the job. Wisdomjobs framed Automatic Storage Management (ASM) interview questions and answers to make it easier for your interview preparation.
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 2. What Are The Key Benefits Of Asm?
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:
Question 3. Describe About Asm Architecture.?
Automatic Storage Management (ASM) instance. Instance that manages the diskgroup metadata
Files that are stored in ASM disk groups are called ASM files, this includes database files
Question 4. How Does Database Connects To Asm Instance?
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.
Question 5. What Init.ora Parameters Does A User Need To Configure For Asm Instances?
The default parameter settings work perfectly for ASM.
The only parameters needed for 11g ASM:
Question 6. How Does The Database Interact With The Asm Instance And How Do I Make Asm Go Faster?
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 7. Do I Need To Define The Rdbms Filesystemio_options Parameter When I Use Asm?
No. The RDBMS does I/O directly to the raw disk devices, the FILESYSTEMIO_OPTIONS parameter is only for filesystems.
Question 8. Why Oracle Recommends Two Disk Groups?
Oracle recommends two disk groups to provide a balance of manageability, utilization, and performance.
Question 9. 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?
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 10. 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?
For 11g ASM/RDBMS it is recommended to use 4MB ASM AU for disk groups. See Metalink Note 810484.1
Question 11. Would It Be Better To Use Bigfile Tablespaces, Or Standard Tablespaces For Asm?
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 12. What Is The Best Lun Size For Asm?
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 :
Using this info , and their standards, the storage folks should build a nice LUN group set for you.
Question 13. In 11g Rac We Want To Separate Asm Admins From Dbas And Create Different Users And Groups. How Do We Set This Up?
Question 14. Can My Rdbms And Asm Instances Run Different Versions?
Yes. ASM can be at a higher version or at lower version than its client databases. There’s two
Diskgroup compatibility attributes:
Question 15. Where Do I Run My Database Listener From; I.e., Asm Home Or Db Home?
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 16. How Do I Backup My Asm Instance?
Not applicable! ASM has no files to backup, as its does not contain controlfile,redo logs etc.
Question 17. When Should I Use Rman And When Should I Use Asmcmd Copy?
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:
Question 18. I’m Going To Do Add Disks To My Asm Diskgroup, How Long Will This Rebalance Take?
Rebalance time is heavily driven by the three items
Question 19. We Are Migrating To A New Storage Array. How Do I Move My Asm Database From Storage A To Storage B?
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.
Note 428681.1 covers how to move OCR/Voting disks to the new storage array
Question 20. 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)?
No. Cross-platform disk group migration not supported. To move datafiles between endian-ness platforms, you need to use XTTS, Datapump or Streams.
Question 21. How Does Asm Work With Multipathing Software?
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 22. Is Asm Constantly Rebalancing To Manage “hot Spots”?
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 23. What Are The File Types That Asm Support And Keep In Disk Groups?
Temporary data files:
Online redo logs:
Question 24. List Key Benefits Of Asm?
Question 25. What Is Asm Striping?
The data extent size is:
ASM stripes files using extents with a coarse method for load balancing or a fine method to reduce latency.
Question 26. How Many Asm Disk Groups Can Be Created Under One Asm Instance?
ASM imposed the following limits:
ASM file size limits (database limit is 128 TB):
Question 27. What Is A Diskgroup?
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.
Question 28. Can My Disks In A Diskgroup Can Be Varied Size? For Example One Disk Is Of 100gb And Another Disk Is Of 50gb. If So How Does Asm Manage The Extents?
Yes, disk sizes can be varied, Oracle ASM will manage data efficiently and intelligent by placing the extents proportional to the size of the disk in the disk group, bigger diskgroups have more extents than lesser ones.
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