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.
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:
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
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.
The default parameter settings work perfectly for ASM.
The only parameters needed for 11g ASM:
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.
No. The RDBMS does I/O directly to the raw disk devices, the FILESYSTEMIO_OPTIONS parameter is only for filesystems.
Oracle recommends two disk groups to provide a balance of manageability, utilization, and performance.
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.
For 11g ASM/RDBMS it is recommended to use 4MB ASM AU for disk groups. See Metalink Note 810484.1
The use of Bigfile tablespaces has no bearing on ASM (or vice versa). In fact most database object related decisions are transparent to 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.
Yes. ASM can be at a higher version or at lower version than its client databases. There’s two
Diskgroup compatibility attributes:
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.
Not applicable! ASM has no files to backup, as its does not contain controlfile,redo logs etc.
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:
Rebalance time is heavily driven by the three items
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
No. Cross-platform disk group migration not supported. To move datafiles between endian-ness platforms, you need to use XTTS, Datapump or Streams.
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.
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).
Temporary data files:
Online redo logs:
The data extent size is:
ASM stripes files using extents with a coarse method for load balancing or a fine method to reduce latency.
ASM imposed the following limits:
ASM file size limits (database limit is 128 TB):
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.
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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Overview Of Administering An Oracle Database
Creating An Oracle Database
Starting Up And Shutting Down
Managing Oracle Database Processes
Managing Control Files
Managing The Redo Log
Managing Archived Redo Logs
Managing Datafiles And Tempfiles
Managing The Undo Tablespace
Using Oracle-managed Files
Using Automatic Storage Management
Managing Space For Schema Objects
Managing Partitioned Tables And Indexes
Managing Hash Clusters
Managing Views, Sequences, And Synonyms
General Management Of Schema Objects
Detecting And Repairing Data Block Corruption
Managing Users And Securing The Database
Managing Automatic System Tasks Using The Maintenance Window
Using The Database Resource Manager
Moving From Dbms_job To Dbms_scheduler
Overview Of Scheduler Concepts
Using The Scheduler
Administering The Scheduler
Distributed Database Concepts
Managing A Distributed Database
Developing Applications For A Distributed Database System
Distributed Transactions Concepts
Managing Distributed Transactions
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