A Recovery Point Objective, or RPO, is the maximum amount of data that can be lost before causing detrimental harm to the organization. RPO indicates the data loss tolerance of a business process or an organization in general. This data loss is often measured in terms of time, for example, 5 hours or 2 days worth of data loss. A zero RPO means that no committed data should be lost when media loss occurs, while a 24 hour RPO can tolerate a day's worth of data loss.
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The most obvious characteristic of the data warehouse is the size of the database. This can be upward of 100's of terabytes. Hardware is the limiting factor to a fast backup and recovery. However, today's tape storage continues to evolve to accommodate the amount of data that must be offloaded to tape (for example, advent of Virtual Tape Libraries which use disks internally with the standard tape access interface). RMAN can fully use, in parallel, all available tape devices to maximize backup and recovery performance.
Essentially, the time required to back up a large database can be derived from the minimum throughput among: production disk, host bus adapter (HBA) and network to tape devices, and tape drive streaming specifications * the number of tape drives. The host CPU can also be a limiting factor to overall backup performance, if RMAN backup encryption or compression is used. Backup and recovery windows can be adjusted to fit any business requirements, given adequate hardware resources.
In a data warehouse, there may be times when the database is not being fully used. While this window of time may be several contiguous hours, it is not enough to back up the entire database. You may want to consider breaking up the database backup over several days. RMAN enables you to specify how long a given backup job is allowed to run. When using BACKUP DURATION, you can choose between running the backup to completion as quickly as possible and running it more slowly to minimize the load the backup may impose on your database.
In the following example, RMAN backs up all database files that have not been backed up in the last 7 days first, runs for 4 hours, and reads the blocks as fast as possible.
BACKUP DATABASE NOT BACKED UP SINCE 'sysdate - 7' PARTIAL DURATION 4:00 MINIMIZE TIME;
Each time this RMAN command is run, it backs up the data files that have not been backed up in the last 7 days first. You do not need to manually specify the tablespaces or data files to be backed up each night. Over the course of several days, all of your database files are backed up.
While this is a simplistic approach to database backup, it is easy to implement and provides more flexibility in backing up large amounts of data. During recovery, RMAN may point you to multiple different storage devices to perform the restore operation. Consequently, your recovery time may be longer.