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1 Introduction to Automatic Storage Management (ASM) Overview of Oracle Automatic Storage Management (ASM) ASM is a volume manager and a file system for Oracle database files ASM is recommended filesystem for RAC and Single instance and it is alternative to conventional volume managers, file systems, and raw devices. ASM is a new type of filesystem which was introduced with Oracle 10g. ASM for storing database files. This provides direct I/O to the file Oracle creates a separate instance for thi
  1 Introduction to Automatic Storage Management (ASM) Overview of Oracle Automatic Storage Management (ASM) ASM is avolumemanager and afile systemfor Oracle database files ASM is recommended filesystem for RAC and Single instance and it is alternative to conventional volume managers,file systems, and raw devices.ASM is a new type of filesystem which was introduced with Oracle 10g. ASM for storingdatabase files. This provides direct I/O to the file Oracle creates a separate instance for this purpose.ASM simplifies administration of Oracle related files by allowing the administrator to referencedisk groups rather than individual disks and files, which are managed by ASM. ASM usesdisk groupsto store datafiles, an ASM disk group is a collection of disks that ASM manages as a unit.You can add or remove disks from a disk group while a database continues to access files fromthe disk group. When you add or remove disks from a disk group, ASM automaticallyredistributes the file contents and eliminates the need for downtime when redistributing thecontent.The ASM volume manager functionality provides flexible server-based mirroring options. TheASM normal and high redundancy disk groups enable two-way and three-way mirroringrespectively. You can use external redundancy to enable a Redundant Array of InexpensiveDisks (RAID) storage subsystem to perform the mirroring protection function.ASM also uses the Oracle Managed Files (OMF) feature to simplify database file management. Benefits of ASM    Provide efficient management of storage    Provide integrated cluster file system and volume management capabilities    Prevents accidental file deletion    Prevents fragmentation and hence no need to relocate data to reclaim space    Available for both single instance and RAC instance    Automatic I/O load balancing as data is striped across disks and better performance    Stripes files rather than logical volumes    Enables online disk reconfiguration and dynamic rebalancing    Provides adjustable rebalancing speed    Provides file based redundancy    Supports only Oracle files    It’s cluster aware What is supported in ASM  Only Oracle files are supported:* Database files* Control files* Online redo log files* Archived redo log files* Flash recovery area files* RMAN files (image copy and backup)These files are NOT supported:* Installation files (in ORACLE_HOME, CRS_HOME)* ORACLE_BASE files( including alert log, trace files, etc)* CRS voting disk and OCR files* Output data from UTL_FILE* Any user or application specific files(e.g. XML or Java files)* Oracle 9i external table files Why ASM ? Some of the storage management features with ASM include    Striping    Mirroring    Asynchronous I/O    Direct I/O    SAME and Load Balancing    Is automatically installed as part of the base code setASM includes striping and mirroring to provide balanced and secure storage. The level of redundancy and the granularity of the striping can be controlled using templates. The new ASMfunctionality can be used in combination with existing raw and cooked file systems, along withOMF and manually managed files. Pre-Requisite for ASM     Need CSS demon for creating an ASM instance(CSS service is responsible for synchronizing ASM and RDBMS instances.)    $ps- ef | grep css    In RAC it is done by Oracle Clusterware    In single instance environment, we have to run#$ORACLE_HOME/bin/localconfig add     Need additional atleast 100M memory for ASM instance  Features of ASM instance    Don’t mount the database but manage metadata requ ired metadata to make ASM filesavailable for DB instance    DB instance access ASM files directly and contact ASM instance only for the layout of ASM files    Smaller than DB instance < 100m    Contains no physical files like logfiles/controlfiles or data files    Requires only the init.ora file for startup    Instance name is +ASM or +ASM 1….n(RAC)  This is the new feature of 10gDATABASE ---  C/R/D files <---- OS ----  Hard disk With the help of OS we are storing into Hard disk.Oracle has given their own file system i.e ASM.If we go with ASM 10 to 15 % performance will increased.DATABASE <------  ASM <------  Hard disk ASM is responsible to store and manage database files such as control, data, redo log files,spfile(not pfile)Archivelog file directly in the hard disk without taking help of OS, why b/c ASM itself acts as afile system. Here hard disk means raw disk(not formatted hard disk) Key points    ASM is free which comes with oracle software.    It acts as a logical volume manager(LVM).    ASM operates on raw device(unformatted SATA Hard disk).    A db can consists ASM files and OS files as well.    We cannot take backup of ASM files by using user managed from OS, with the help of oracle utilites such as OEM, RMAN we can take backup of ASM database files.    Root directory of ASM is + .Oracle uses two instances1.   RDBMS instance2.   ASM instance ASM Instance  ASM instance is a special type of oracle instance that are responsible to store and manage ASMfiles which are present in the ASM disk groups.An ASM has a SGA and background processes that are similar to those of Oracle Database.However, because ASM performs fewer tasks than a database, an ASM SGA is much smaller than a database SGA. In addition, ASM has a minimal performance effect on a server. ASMinstances mount disk groups to make ASM files available to database instances.  ASM instancesdo not mount databases. ASM metadata is the information that ASM uses to control a disk group and the metadata resideswithin the disk group. ASM metadata includes the following information:    The disks that belong to a disk group    The amount of space that is available in a disk group    The filenames of the files in a disk group    The location of disk group datafile data extents    A redo log that records information about atomically changing data blocksASM and database instances require shared access to the disks in a disk group. ASM instancesmanage the metadata of the disk group and provide file layout information to the databaseinstances.ASM instances can be clustered using Oracle Clusterware; there is one ASM instance for eachcluster node. If there are several database instances for different databases on the same node,then the database instances share the same single ASM instance on that node.If the ASM instance on a node fails, then all of the database instances on that node also fail.Unlike a file system failure, an ASM instance failure does not require restarting the operatingsystem. In an Oracle RAC environment, the ASM and database instances on the surviving nodesautomatically recover from an ASM instance failure on a node. ASM Disk Groups A disk group consists of multiple disks and is the fundamental object that ASM manages. Eachdisk group contains the metadata that is required for the management of space in the disk group.Files are allocated from disk groups. Any ASM file is completely contained within a single disk group. However, a disk group might contain files belonging to several databases and a singledatabase can use files from multiple disk groups. For most installations you need only a smallnumber of disk groups, usually two, and rarely more than three. Mirroring and Failure Groups Mirroring protects data integrity by storing copies of data on multiple disks. The disk group typedetermines the mirroring levels with which Oracle creates files in a disk group.
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