ASM Architecture

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ASM Architecture

Automatic Storage Management is the storage solution from Oracle.The ASM has an instance architecture.The OS process establlishes,maintains it.


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  • Submitted By - positive fanatic

  • Submitted on - 2008-07-07 14:17:23


ASM instance is used to manage database files.If a node hosts multiple databases,single database,files can be managed using ASM.<br /><br />Two possible ASM deployments are:<br />1) Seperate oracle home is there are multiple databases on a single node<br />2) No seperate oracle home if the node hosts a single database.<br /><br />ASM instance needs to be created and started before the Oracle database instance is started.<br /><br />css - cluster synchronization service daemon is used to establish connection between an ASM instance and oracle database instance.<br /><br />To startup ASM instance alone and restrict the connection to Oracle database instance startup ASM instance as follows:<br />SQL>STARTUP RESTRICT;<br /><br />Steps to startup an ASM instance are as follows:<br /><br />1) Check is css is running using<br />ps -efgrep css<br /><br />We can also use crsctl command to check if css appears healthy<br />crsctl check css<br /><br />If css isn't up and running startup ASM as follows<br />1) Login as root user<br />2) export PATH=PATH:$ORACLE_HOME<br />3) localconfig add<br /><br />The localconfig command creates /etc/oracle file,startsup css.The $ORACLE_HOME/css/admin has control script for css startup and shutdown.<br /><br />It adds init.cssd to /etc/inittab file.<br /><br />If we use DBCA to create an instance css is started automatically.<br /><br />2) Create a initialization parameter file initasm+.ora with the following parameters set.<br /><br />Instance_type=+ASM<br />ASM_POWER_Limit =Value from 1 to 11<br />ASM_Diskstring = '/dev/sda*',<br />ASM_DISKGROUPS=dg1,dg2<br /><br />3) Startup the instance.ASM doesn't have a data dictionary.It is mandatory to login as a user with SYSDBA/SYSOPER privilege.<br />For local authentication use Operating system(OS) authentication.<br />For remote authentication use a password file.<br /><br />4) Set ORACLE_SID=+ASM (ASM is the default value).The value set for instance_type is mapped internally to db_unique_name.<br /><br />$sqlplus / nolog<br />SQL>connect / as sysdba<br />SQL> startup pfile='/asd/initasm+.ora'<br /><br />This step creates an ASM instance.ASM cache is the SGA component specific to ASM.It takes as little as 25MB- 30MB space.Total spce needed for an ASM instance is 100MB as it doesnt have any datafiles.<br /><br />5) Check is ASM instance is up and running using :<br /><br />ps -efgrep asm<br /><br />The step above lists background processes like:<br /><br />asm_pmon_+asm<br />asm_smon_+asm<br />asm_lgwr_+asm<br />asm_ckpt_+asm<br />asm_dbw0_+asm<br />asm_mman_+asm<br /><br />Few special is ASM like<br /><br />asm_rbal_+asm<br />asm_psp0_+asm<br />asm_gmaon_+asm<br /><br />For more details and lots of interesting articles visit:<br /><br /><br />For further details mail to    More detail...

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