We've had a database crash yesterday, so we restore all datafiles from tape (offline backup) and recover the database.
The recovery was successfully but there are several error messages in the alert.log file during recovery:

alert.log
=========
ALTER DATABASE RECOVER CONTINUE DEFAULT
Media Recovery Log /orabaan/archive/T0001S0000009730.ARC
Tue Jan 30 22:22:01 2001
Errors in file /orabaan/oracle/product/7.3.4/rdbms/log/ora_4727.trc:


ora_4727.trc
============
***
Corrupt block dba: 0x94026ea0 file=37. blocknum=159392. found during media/insty
on disk type:0. ver:1. dba: 0x00000000 inc:0x00000000 seq:0x00000000 incseq:0x00
Reread of block=94026ea0 file=37. blocknum=159392. found different data
***
Corrupt block dba: 0x94026ea0 file=37. blocknum=159392. found during reread
on disk type:0. ver:0. dba: 0x00000000 inc:0x00000000 seq:0x00000000 incseq:0x1c
*** 2001.01.30.22.22.01.572
Recovery is repairing media corrupt block 159392 of file 37
***


Where are these errors coming from ???

Hubertus