Veritas File System 5.1 SP1 Administrator"s Guide (5900-1499, April 2011)

About supporting many concurrent I/Os in one system call
When performing asynchronous I/O, an Oracle process may try to issue additional
I/O requests while collecting completed I/Os, or it may try to wait for particular
I/O requests synchronously, as it can do no other work until the I/O is completed.
The Oracle process may also try to issue requests to different files. All this activity
can be accomplished with one system call when Oracle uses the Oracle Disk
Manager I/O interface. This interface reduces the number of system calls
performed to accomplish the same work, reducing the number of user space/kernel
space context switches.
About avoiding duplicate file open calls
Oracle Disk Manager allows files to be opened once, providing a “file identifier.”
This is called “identifying” the files. The same file identifiers can be used by any
other processes in the Oracle instance. The file status is maintained by the Oracle
Disk Manager driver in the kernel. The reduction in file open calls reduces
processing overhead at process initialization and termination, and it reduces the
number of file status structures required in the kernel.
About allocating contiguous datafiles
Oracle Disk Manager can improve performance for queries, such as sort and
parallel queries, that use temporary tablespaces. Without Oracle Disk Manager,
Oracle does not initialize the datafiles for the temporary tablespaces. Therefore,
the datafiles become sparse files and are generally fragmented. Sparse or
fragmented files lead to poor query performance. When using Oracle Disk Manager,
the datafiles are initialized for the temporary tablespaces and are allocated in a
contiguous fashion, so that they are not sparse.
About Oracle Disk Manager and Storage Foundation
Cluster File System
Oracle Disk Manager supports access to clustered files in the SFCFS environment.
With a Veritas Storage Foundation Cluster File System license, ODM supports
SFCFS files in a serially-exclusive mode which allows access to each SFCFS file
by one node at a time, but does not allow simultaneous access from multiple nodes.
About Oracle Disk Manager and Oracle Managed Files
Oracle10g or later offers a feature known as Oracle Managed Files (OMF). OMF
manages datafile attributes such as file names, file location, storage attributes,
Using Veritas Extension for Oracle Disk Manager
About Oracle Disk Manager and Storage Foundation Cluster File System
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