There usually comes a point during the lifecycle of the data when it is no longer being regularly accessed and is considered eligible for archiving. Traditionally, the data would have been removed from the database and stored on tape, where you can store vast quantities of information for a very low cost. Today, it is no longer necessary to archive that data to tape, instead it can remain in the database, or be transferred to a central online archive database. All this information can be stored using low-cost storage devices whose cost per gigabyte is very close to that of tape.
There are multiple benefits to keeping all of the data in an Oracle Database for archival purposes. The most important benefit is that the data always be instantly available. Therefore, time is not wasted locating the tapes where the data was archived and determining whether the tape is readable and still in a format that can be loaded into the database.
If the data has been archived for many years, then development time may also be needed to write a program to reload the data into the database from the tape archive. This could prove to be expensive and time consuming, especially if the data is extremely old. If the data is retained in the database, then this is not a problem, because it is online, and in the latest database format.
Holding the historical data in the database no longer impacts the time required to backup the database and the size of the backup. When RMAN is used to back up the database, it only includes in the backup the data that has changed. Because historical data is less likely to change, after that data has been backed up, it is not backed up again.
Another important factor to consider is how the data is to be physically removed from the database, especially if it is to be transferred from a production system to a central database archive. Oracle provides the capability to move this data rapidly between databases by using transportable tablespaces or partitions, which moves the data as a complete unit.
When it is time to remove data from the database, the fastest way is to remove a set of data. This is achieved by keeping the data in its own partition. The partition can be dropped, which is a very fast operation. However, if this approach is not possible because data relationships must be maintained, then a conventional SQL delete statement must be issued. You should not underestimate the time required to issue the delete statement.
If there is a requirement to remove data from the database and there is a possibility that the data may need to be returned to the database in the future, then consider removing the data in a database format such as a transportable tablespace, or use the XML capability of Oracle Database to extract the information in an open format.
Consider an online archive of your data into Oracle Database for the following reasons:
The cost of disk is approaching that of tape, so you can eliminate the time to find the tape that contains the data and the cost of restoring that data
Data remains online when needed, providing you faster access to meet business requirements
Data online means immediate access, so fines by regulatory body for failing to produce data are less likely
The current application can be used to access the data, so you do not need to waste resources to build a new application