10.2 How the Oracle Tuxedo System Manages Files

The Oracle Tuxedo system provides a facility called the Disk Management Interface (DMI), which manages logical files within a single disk device or set of devices. The DMI performs tasks such as storing binary configuration tables and the transaction log. You can use it to create, initialize, or destroy entries in the Oracle Tuxedo filesystem. To access the DMI, use the tmadmin(1) administrative commands described in the Oracle Tuxedo Command Reference. There are two ways that the logical files managed by the DMI can be stored physically:

• Stored on an operating-system (OS) filesystem
• Stored on disk space, set aside for the Oracle Tuxedo system, that is outside the control of all OS filesystems

Oracle Tuxedo files reside on device special files in the designated space and are managed directly by the DMI disk management software. The DMI supports the notion of an Oracle Tuxedo filesystem distinct from any OS filesystem.

Space outside the OS filesystem is usually referred to as raw disk space. Not only is I/O faster when done by system calls reading directly from and writing directly to device special files on raw disks, but a physical write() occurs right away.

When using an OS filesystem, Oracle Tuxedo cannot predict or control the precise moment at which awrite() is done. When using raw disk space, however, Oracle Tuxedo has accurate control of the write operation, which is particularly important for entries in the Oracle Tuxedo transaction log. Also, when multiple users are accessing the system, being able to control the write operation is important for assuring database consistency.