Instance Recovery Vs Media Recovery

Instance Recovery: 

Instance recovery is done automatically by SMON. it is reqd in case of abonormal shutdown such as shutdown abort or any such reason.
Instance recovery is recovery of a single database instance. It is also called crash recovery if ur database has only instance.
Crash recovery is recovery of all instances in database.

 Instance recovery refers to the case where a surviving instance recovers a failed instance in an Oracle Real Application Clusters database.

Media Recovery:

Media recovery is divided into the following types:

• Datafile media recovery
• Block media recovery

Typically, the term "media recovery" refers to recovery of datafiles. Block media recovery is a more specialized operation that you can only perform with RMAN.

• Datafile media recovery is used to recover from a lost or damaged current datafile or control file. 

• Block media recovery is a technique for restoring and recovering individual data blocks while all database files remain online and available. If corruption is limited to only a few blocks among a subset of database files, then block media recovery may be preferable to datafile recovery.

Crash Recovery:

Crash recovery is used to recover from a failure either when a single-instance database crashes or all instances of an Oracle Real Application Clusters database crashes.