Automatic Storage Management (ASM) is an oracle’s logical volume manager, it uses OMF (Oracle Managed Files) to name and locate the database files. It can use raw disks, filesystems or files which can be made to look like disks as long as the device is raw. ASM uses its own database instance to manage the disks, it has its own processes and pfile or spfile, it uses ASM disk groups to manage disks as one logical unit.
The benefits of ASM are
1- ASM Instance: Is a special instance that does not have any data files, there is only ASM instance one per server which manages all ASM files for each database. The instance looks after the disk groups and allows access to the ASM files. Databases access the files directly but uses the ASM instance to locate them. If the ASM instance is shutdown then the database will either be automatically shutdown or crash.
2- ASM Disk groups: Disks are grouped together via disk groups, these are very much like logical volumes.
3- ASM Files: Files are stored in the disk groups and benefit from the disk group features i.e. stripping and mirroring.
File types that can be managed by ASM:
Data files, Control files, Redo log files, SPFILE , RMAN backup files, Archived redo log files and FRA files.
ASM Processes in ASM instance:
1- RBAL( Re-BALancer): Coordinates the re-balancing activity when a new disk added or removed.
2- ARBn(Actual Rebalancer): Do the actual data movement requested by RBAL. n 1..9.
ASM Processes in Database instance:
1- RBAL( Re-BALancer): Open and Close ASM disks.
2- ASMB: Connect to the ASM channel and do communication between ASM and RDBMS instances. The requests through this could be file creation, deletion , resizing and various statistics and status messages.
ASM registers its name and disks with the RDBMS via the cluster synchronization service (CSS).
This is why CSS needed even not on clustered environment.
The benefits of ASM are
- Provides automatic load balancing over all the available disks, thus reducing hot spots in the file system
- Prevents fragmentation of disks, so you don't need to manually relocate data to tune I/O performance
- Adding disks is straight forward - ASM automatically performs online disk reorganization when you add or remove storage
- Uses redundancy features available in intelligent storage arrays
- The storage system can store all types of database files
- Using disk group makes configuration easier, as files are placed into disk groups
- ASM provides stripping and mirroring (fine and coarse gain - see below)
- ASM and non-ASM oracle files can coexist
- ASM is free!!!!!!!!!!!!!
1- ASM Instance: Is a special instance that does not have any data files, there is only ASM instance one per server which manages all ASM files for each database. The instance looks after the disk groups and allows access to the ASM files. Databases access the files directly but uses the ASM instance to locate them. If the ASM instance is shutdown then the database will either be automatically shutdown or crash.
2- ASM Disk groups: Disks are grouped together via disk groups, these are very much like logical volumes.
3- ASM Files: Files are stored in the disk groups and benefit from the disk group features i.e. stripping and mirroring.
File types that can be managed by ASM:
Data files, Control files, Redo log files, SPFILE , RMAN backup files, Archived redo log files and FRA files.
ASM Processes in ASM instance:
1- RBAL( Re-BALancer): Coordinates the re-balancing activity when a new disk added or removed.
2- ARBn(Actual Rebalancer): Do the actual data movement requested by RBAL. n 1..9.
ASM Processes in Database instance:
1- RBAL( Re-BALancer): Open and Close ASM disks.
2- ASMB: Connect to the ASM channel and do communication between ASM and RDBMS instances. The requests through this could be file creation, deletion , resizing and various statistics and status messages.
ASM registers its name and disks with the RDBMS via the cluster synchronization service (CSS).
This is why CSS needed even not on clustered environment.
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