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http://neworacledba.blogspot.com Plenty of useful articles on oracle, oracle dba, oracle RAC (Real Application cluster) DBA, Oracle dataguard, certification exam dumps, shell script, UNIX/LINUX/SOLARIS, PMP (Project Management Professional), ITIL(Infrastructure Information Library), ISO/IEC 20000 and many more….. What is ASM? ASM is a Volume Manager and a file system for Oracle Database Files that supports single instance Oracle Database and Oracle Real Application cluster (RAC) configuration. What is the recommended storage management solution from Oracle?Why? ASM is the recommended storage management solution from oracle as it provides an alternative to conventional volume managers,file systems and raw devices. How is datafile stored in ASM? ASM uses disk groups to store data files. What is an ASM disk group? An ASM disk group is a group of disks that ASM manages as an unit.Within the diskgroups an file system interface maintains the Oracle database files. ASM simplifies database storage by consolidating disks into disk groups.This reduces I/O overhead. How is the performance of disk group comparable to raw disks?/Are disk groups a good alternative to raw disks? The files distributed across the set of disks in a disk group are striped or distributed across the disks to eliminate hot spots and improve performance.Thus they perform equally well as raw disks. How does ASM eliminate downtime? Disks can be added and removed from the disk groups online,(i.e)during the operation of the database without any downtime. When disks are added or removed ASM automatically redistributes the contents without any downtime.Thus ASM eliminates downtime. Give details on server-based mirroring:This is a flexible option provided by ASM. The normal and redundant options of ASM provides two and three way mirroring. We can use external option to enable RAID(Redundant Array Of Independent Disks). How does an ASM manage files?/How is the file management simplified using ASM? ASM uses the Oracle Managed Files(OMF) feature which simplifies file management.Files are created at specified location,renames files,deletes files when operations at tablespace level happens(say tablespace deletion). Give some interfaces used to manage ASM:Oracle Enterprise Manager(OEM),SQL*PLUS,ASMCMD command-line interface are some interfaces that can be used with ASM.
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Visit : http://neworacledba.blogspot.com Can ASM co-exist with non-ASM system:Yes,ASM can co-exist with non-ASM third-party file systems and thus can be integrated into pre-existing environments.OEM has an interface for migrating non-ASM files to ASM. What is an ASM instance? An ASM instance is the instance that manages ASM disk groups. It composes of System Global Area(SGA) and background processes. ASM instance mounts a disk group that is made available to the database instance. An ASM instance manages the metadata of a disk group and provides file layout information to the database instances. Will the SGA(System Global Area) of ASM is comparable in size to an Oracle database instance? No.The SGA size of an ASM is smaller than that of an Oracle database instance,as an ASM performs fewer tasks than a database. Can ASM instance mount a database? No.An ASM instance can mount a disk group that can be used by a database instance. What is ASM metadata and where is it present? ASM metadata is the information that ASM uses to control the disk group.It is present within a disk group. What is an ASM metadata composed of? An ASM metadata includes the following: 1) The disks that belong to a disk group 2) Amount of space available within a disk group 3) The filenames of the files within a disk group 4) The location of disk group datafile data extents 5) A redo log that records information about automatically changing data blocks What are the possible ASM configurations? ASM and database instances share access to disks in a disk group. 1) There can be one ASM instance and one database instance serving single database in a node 2) There can be one ASM instance,multiple database instances serving many database in a node. If the ASM instance fails,all the databases fails.The advantage is that this doesn't demand a Server reboot(Operating system restart) 3) There can be clustered ASM instances that are clustered using Oracle Clusterware.(i.e)One ASM instance on each node that are integrated using Oracle clusterware.
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Visit : http://neworacledba.blogspot.com How does an ASM instance communicate with a database instance? The ASM instance manages the metadata and provides space allocation for the ASM files.When a database instance creates or opens an ASM file,it communicates those requests to the ASM instance.In response the ASM instance provides the file extent map information to the database instance. Visit : http://neworacledba.blogspot.com