Veritas Storage Foundation™ for Oracle 5.0.1 Administrator's Guide

DB2), where data is stored in tables and generally accessed by one or more keys
and Flat File Databases, where data is not generally broken up into tables and
relationships. Databases generally provide tools and/or interfaces to retrieve data.
datafile A physical database attribute that contains database data. An Oracle datafile can
only be associated with a single database. One or more datafiles form a logical
database storage unit called a tablespace.
DCO See "data change object (DCO)."
DCO log volume A volume used to hold persistent FastResync change maps.
Decision Support
Systems
Decision Support Systems (DSS) are computer-based systems used to model,
identify, and solve problems, and make decisions.
defragmentation The act of reorganizing data to reduce fragmentation. Data in file systems become
fragmented over time.
device file A block- or character-special file located in the /dev directory representing a
device.
device name The name of a device file, which represents a device. AIX syntax is Disk_#; HP-UX
syntax is c#t#d#; Linux syntax is sda, where "a" could be any alphabetical letter;
Solaris syntax is c#t#d#s#.
direct I/O An unbuffered form of I/O that bypasses the kernel’s buffering of data. With direct
I/O, data is transferred directly between the disk and the user application.
Dirty Region Logging The procedure by which the Veritas Volume Manager monitors and logs
modifications to a plex. A bitmap of changed regions is kept in an associated
subdisk called a log subdisk.
disk access name The name used to access a physical disk, such as Disk_1 on an AIX system, c1t1d1
on an HP-UX system, sda on a Linux system, or c0t0d0s0 on a Solaris system. The
term device name can also be used to refer to the disk access name.
disk array A collection of disks logically and physically arranged into an object. Arrays
provide benefits including data redundancy and improved performance.
disk cache A section of RAM that provides a cache between the disk and the application. Disk
cache enables the computer to operate faster. Because retrieving data from hard
disk can be slow, a disk caching program helps solve this problem by placing
recently accessed data in the disk cache. Next time that data is needed, it may
already be available in the disk cache; otherwise a time-consuming operation to
the hard disk is necessary.
disk group A collection of disks that share a common configuration.
A disk group configuration is a set of records containing detailed information on
existing Veritas Volume Manager objects (such as disk and volume attributes) and
their relationships. Each disk group has an administrator-assigned name and an
403Glossary