Computers and storage devices are full of data and there are many different forms of data depending on how often the data is accessed or changed. Persistent data is data that is not normally accessed and rarely changed. Persistent database data is typically stored on a server and is accessed more frequently than archived data. With data archived or stored on disk or tape, the information is rarely opened or used. In addition to archiving the data, this allows researchers to examine old or stored information to find past trends that can be applied to current situations.
Persistent data is usually archived to prevent it from clogging up the local hard drive.
Persistent data rarely changes; this means that the information stored on the database, disk, or tape is not changed except on special occasions. Accessed information is more common than modified information, but it is rarely done. This data also exists from one session to the next, unlike data types that only exist for one session and then are deleted or linked to that single session.
With database persistent data, an entire database or section of a database is created to hold the archived data. This can be done locally, in a database stored on the computer’s hard drive, or it can be placed on a server. This persistent information is accessed more frequently than the tape and disk variants because the information is readily available. At the same time, this database will typically remain intact for months or years.
Persistent data on tape and disk should not be touched, or even loaded into a computer, for years. This data is strictly for archival purposes and is rarely accessed. Persistent data is often large, so it is often erased from the local hard drive as soon as the data is archived, so tape or disk is often the only copy of the data.
There are several reasons why a developer or administrator might want to archive persistent data. While the information may not be current or useful at this time, the data may be useful later for researchers, or it may be helpful in finding a trend based on old information. Another reason is to reduce digital clutter on the hard drive. Hard drives need space to function, and large blocks of persistent data can easily take up an entire hard drive. To avoid a full hard drive, the administrator will archive unused data.
