Datasheet

Working with the ASM Instance 3
Here are some features of ASM:
Automatic software data striping (RAID-0)
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Load balancing across physical disks
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Software RAID-1 data redundancy with double or triple mirrors
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Elimination of fragmentation
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Simplification of file management via support for Oracle Managed Files (OMF)
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Ease of maintenance
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ASM fits perfectly into a Real Application Clusters (RAC) environment, but you can use
ASM in a non-RAC environment too. In the following sections we will cover these ASM-
related topics:
The ASM instance
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Configuring ASM disks
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Accessing ASM from the database
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Managing ASM
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ASM data dictionary views
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You should be aware of a few ASM limitations:
ASM limits you to 63 disk groups in a given storage system. A disk group is a logical
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storage entity that is made up of one or more physical disks (we discuss adding ASM
disk groups later in this chapter).
You can have a maximum of 10,000 ASM disks in a given storage system.
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Each ASM disk can be a maximum of 4 petabytes (PB) in size.
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Each ASM instance can manage up to 40 exabytes of storage.
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Each disk group can contain up to one million files.
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Maximum file sizes vary by the type of disk group:
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External-redundancy disk group: 140PB maximum file size
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Normal-redundancy disk group: 42PB maximum file size
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High-redundancy disk group: 15PB maximum file size
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Working with the ASM Instance
Driving ASM is the ASM instance, which is a separate instance from any database instance.
The ASM instance is mounted but never open like an Oracle database. It is, essentially, just
a bunch of programs (daemons) running. You will create only one ASM instance per node.
You can use the Oracle Database Configuration Assistant (DBCA) to create the ASM
instance for you, or you can choose to create the ASM instance yourself.
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