Hello,

Firstly, have you know that this error should not give any problems for Oracle itself (even on start) nor to RMAN operations.

So, without blabbing more, we have this error on dbfsize command:

$ dbfsize system01.dbf
system01.dbf: Header block magic number is bad; trying raw file format...
system01.dbf: Header block magic number is bad

To double check it and be sure the file is ok, you can verify it with dbv:

$ dbv FILE=system01.dbf

DBVERIFY: Release 10.2.0.4.0 - Production on Tue Feb 26 16:37:02 2013

Copyright (c) 1982, 2007, Oracle.  All rights reserved.

DBVERIFY - Verification starting : FILE = system01.dbf


DBVERIFY - Verification complete

Total Pages Examined         : 140800
Total Pages Processed (Data) : 79455
Total Pages Failing   (Data) : 0
Total Pages Processed (Index): 35549
Total Pages Failing   (Index): 0
Total Pages Processed (Other): 380
Total Pages Processed (Seg)  : 0
Total Pages Failing   (Seg)  : 0
Total Pages Empty            : 25416
Total Pages Marked Corrupt   : 0
Total Pages Influx           : 0
Highest block SCN            : 1198910981 (1.1198910981)

Solution:

The correction is simple and can be done with the RESIZE command within Oracle:

ALTER DATABASE DATAFILE '/oracle/DBPROD/system/system01.dbf' RESIZE 1100M;

Now you should have the correct output:

$ dbfsize system01.dbf
Database file: system01.dbf
Database file type: file system
Database file size: 140800 8192 byte blocks