One of the principle designs of Oracle Database 10g is ease of management of the database freeing the DBA to perform other tasks. In this light, Oracle introduced Automated Storage Management (ASM) in Oracle Database 10g to simplify database file administration. Database environments have become more and more complex, with large number of data files, SAN's, JBODs and high availability requirements. Like a logical volume manager, Oracle allows you to reduce the management of Oracle files into ASM disk groups.

ASM stores files in disk groups, which are logical entities made up of one or more physical disk drives assigned to that disk group. You can store datafiles, online redo logs, archived redo logs and control files. Additionally Oracle Database 10g allows you to create the flash recovery area on an ASM disk group, so your backups to disk can be made to ASM.

Oracle touts several features associated with ASM including:

  • Automatic software data striping (RAID 0)
     
  • Load balancing across physical disks
     
  • Software RAID 1 data redundancy with double or triple mirrors
     
  • Elimination of fragmentation
     
  • Elimination of file management
     
  • Ease of maintenance

ASM fits perfectly into a RAC environment, but you can use ASM in a non-RAC environment too. The topics in this section cover the following ASM related subjects:

Note that this article does not cover system level administrative issues, such as configuring a cluster, setting up a SAN or partitioning disks. In this article we assume that these tasks have been done already.

What about ASM limitations? There are a few that you may want to consider:

  • ASM limits you to 63 disk groups in a given storage system. A disk group is a logical storage entity that is made up of one or more disks (see Adding ASM disk groups for more information).
  • You can have up to a maximum of 10,000 ASM disks in a given storage system.

  • Each ASM disk can be up to a maximum of 4 petabytes in size.

  • Each ASM instance can manage up to 40 Exabytes of storage.

  • Each disk group can contain up to one million files

  • Maximum file sizes vary on the type of disk group:

    • External redundancy disk group 35 TB Maximum file size
       
    • Normal redundancy disk group 5.8 TB maximum file size
       
    • High redundancy disk group 3.9 TB maximum file size

The ASM Instance

Driving ASM is the ASM instance. The ASM instance is a separate instance, that is mounted but never has a database associated with it. You will only create one ASM instance per node. The Oracle Database Configuration Assistant (DBCA) can be used to create the ASM instance for you, or you can choose to create the ASM instance yourself. See the following topics for detailed information on the ASM Instance: