Oracle distinguishes between a restartable and a recoverable state of the database, that correlates to a restart and recovery solutions respectively.
A restartable state requires all redo logs, data, and control files to be consistent with each other. There is no use of archive logs in a restartable solution. When the Oracle database starts and the database files are consistent (in a restartable state), it automatically goes through crash/instance recovery without user intervention. During that process, the database engine re-applies committed transactions using the redo log files and removes uncommitted transactions using the undo log files. At the end of the process the database opens, ready for transactions. The data in the database after it opens from a restartable state represents the exact point in time when the restartable state was created, be it a power-failure, a storage consistent snapshot, or the point in time when consistent storage replication stopped replicating data.
A recoverable state of the database relies on a manual process called media recovery in which archive logs are applied to an older version of the datafiles. That older version is referred to as a database backup copy and is typically created using Oracle Recovery Manager (RMAN) or a storage snapshot taken while the database is quiesced (Oracle ‘hot-backup’ mode). That image only contains the Oracle datafiles.
Except for a cold backup, where the database is shutdown first, a recoverable state is created while the database is open, and therefore, the datafiles are in a ‘fuzzy’, or inconsistent state. During media recovery, the archive logs are applied to the datafiles from the last point of the datafiles consistency (the last complete database checkpoint), and until all the datafiles are consistent again. Additional archive logs can be applied to bring the database closer to the present time, where if the online redo logs are available, they can also be applied to provide a no-data-loss solution.
Note: Oracle restart solution does not require archive logs and recovery solution does. Oracle restart solution opens the database to the point in time when the restartable state was created and recovery solution applies available logs to bring the database forward in time, up to a possible no-loss of all committed transactions. However, Oracle restart solution requires the data, control, and redo logs files, while a recovery solution requires an older version of just the datafiles, together with more recent archive logs and optionally redo logs.