Mixing an active
Unix file system with an active Oracle raw device will cause I/O
performance problems.
Most operating systems that support raw devices also provide a logical volume management
layer that allows administrators to perform file system commands for the raw devices. This
approach allows you to have the benefits of file system management along with the performance
benefits of raw devices. If you are planning to use raw devices, you should use a logical volume
management tool to simplify the system management.
Using Automatic Storage Management
As of Oracle 10g, you can use Automatic Storage Management (ASM) to manage your database
storage area. See Chapter 4 for a detailed analysis of how ASM can provide most of the
performance benefits of raw devices with the ease of use of a traditional operating system
file system, along with numerous examples.
When creating a new tablespace or other database structure in an ASM environment, such
as a control file or redo log file, you can specify a disk group as the storage area for the database
structure instead of an operating system file. ASM takes the ease of use of Oracle-Managed Files
(OMF) and combines it with mirroring and striping features to provide a robust file system and
logical volume manager that can even support multiple nodes in an Oracle Real Application
Cluster (RAC). ASM eliminates the need to purchase a third-party logical volume manager.
ASM not only enhances performance by automatically spreading out database objects over
multiple devices, but also increases availability by allowing new disk devices to be added to the
database without shutting down the database; ASM automatically rebalances the distribution of
files with minimal intervention.
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