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ASM - Automatic Storage Management


ASM - Automatic Storage Management
Is a LVM   (Logical Volume Manager) that provides storage abstraction layer
The  RDBMS  see only Diskgroups (set of  RAW disks )
Can’t  store binaries on Diskgroups
Uses OMF (Oracle Managed Files)

Striping
  • Coarse - 1MB allocation units | OLTP | small IO
  • Fine - 128 kb allocation units | Data warehouses | high IO
Allows three Redundancy types
  • High
  • Normal
  • External
Installed in separated dedicated instance (+ASM) as part of Grid Infrastructure
No DB or data dictionary => +ASM instance will be mount never open
  • Where the users are saved?  Password file.
Managed by users with SYSASM role
Specific processes
  • RBAL - Coordinates disk activity for disk groups (Rebalance Master) 
  • ARBn - Perform the extent movement (Rebalance "Slave")
  • ASMB -  Perform the communication between database and the ASM instance
ASM  + RMAN
  • Backup ASM disks
  • Migrate databases from OS filesystem to ASM
ASM Utility
  • ASMCMD
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