Open oracle db with broken Redo-Log-Blockheader - database

Question

We have a database for developers. A handful of records that are missing are uncritical. It should only be the database available again and that is my goal.
The state of the database is as follows:
SQL> select instance_name, version, status from v$instance;
INSTANCE_NAME VERSION STATUS
---------------- ----------------- ------------
ora12 12.2.0.1.0 MOUNTED
If I try to open the database, it failes as:
SQL> alter database open;
alter database open
*
FEHLER in Zeile 1:
ORA-00354: Fehlerhafter Redo-Log-Blockheader
ORA-00353: Logfehler bei Block 14876, Verõnderung von 14597665 Zeit 01/13/2018 17:17:33
ORA-00312: Online-Log 1, Thread 1: 'C:\ORACLE\DBADMIN\VIRTUAL\ORADATA\ORA12\REDO01.LOG'
As mentioned before: A small data loss is not relevant for this database. How can I open the database?
Edit because of the suggestion of kfinity:
I try the suggestions from kfinity with the following outcome.
C:\Windows\System32>sqlplus / as sysdba
SQL*Plus: Release 12.2.0.1.0 Production on Do Feb 1 15:54:20 2018
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Verbunden mit:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
SQL> select instance_name, version, status from v$instance;
INSTANCE_NAME VERSION STATUS
---------------- ----------------- ------------
ora12 12.2.0.1.0 MOUNTED
SQL> recover database until cancel;
ORA-00279: ???nderung 14597437, erstellt von . Erforderlich f??r Thread 1
Log angeben: {<RET>=suggested | filename | AUTO | CANCEL}
CANCEL
ORA-01547: Warnung: RECOVER erfolgreich, doch OPEN RESETLOGS w??rde folgenden
Fehler ergeben
ORA-01194: Datei 1 erfordert weiteres Recovery, um konsistent zu werden
ORA-01110: Datendatei 1: 'C:\ORACLE\DBADMIN\VIRTUAL\ORADATA\ORA12\SYSTEM01.DBF'
ORA-01112: Media Recovery nicht gestartet
SQL> ALTER Database open resetlogs;
ALTER Database open resetlogs
*
FEHLER in Zeile 1:
ORA-00603: ORACLE server session terminated by fatal error
ORA-01092: ORACLE instance terminated. Disconnection forced
ORA-00600: internal error code, arguments: [4194], [32], [21], [], [], [], [],
[], [], [], [], []
Prozess-ID: 1480
Session-ID: 250 Seriennummer: 46338
Am I right, that the database is damaged beyond repair?

Answer 1

The fix to "ORA-00354: corrupt redo log block header" is to clear the log file with the problem and then immediately take a full backup, since you'll have a gap in your redo history and won't be able to recover:
alter database clear unarchived logfile 'C:\ORACLE\DBADMIN\VIRTUAL\ORADATA\ORA12\REDO01.LOG';
As this article points out, if your log files are multiplexed (which they should be - keeping multiple copies on separate disks helps avoid corruption issues like this), then you can simply replace the corrupted redo log file with a clean copy of the same file from one of the other locations.
Edit: if it won't let you clear a logfile because it's needed for recovery, then you need to do incomplete media recovery, where you basically only recover up until the corrupt redo logs (and throw the rest out). There are detailed guides on how to do this, but the basic idea is to do:
RECOVER DATABASE UNTIL CANCEL;
Which will let you apply the good redo logs to the current database state. Once you've gotten up to the corrupt one, you CANCEL and do:
ALTER DATABASE OPEN RESETLOGS;
Which discards the rest of the unapplied changes and resets the database to the last consistent state (SCN) you have.