System Administrator’s Guide U42252-J-Z915-1-76

Introduction Function Scope
these redolog files had already been saved on the backup medium by the
archiving monitor and then automatically deleted, they will be read in again and
reapplied until the database is up to date. The database is then opened and is
again ready for normal operation. The recovery is triggered by the ora_recut and
nsrora_rec commands and proceeds automatically; a knowledge of ORACLE is
not necessarily required for this (see also chapter “Recovery”).
2.5 Function Scope
Physical faults that bring normal database operation to a halt basically fall into
the following four categories:
●loss of a (all) control file(s)
●loss of a current online redolog file
●loss of files containing system data
●loss of files containing user data.
As a rule, the loss of a control file does not pose major problems because the
control file can be mirrored at the software level using the control_files parameter
in the ORACLE parameter file init<ORACLE_SID>.ora. ORACLE strongly
recommends saving at least two copies of the control file on different disks. We
agree with this recommendation.
The loss of a current online redolog file is also precluded almost completely by
mirroring (at the software level by ORACLE or at the hardware level by mirror
disks).
For this reason, neither of these fault categories (loss of the control file
and loss of current online redolog files) is taken into account during an
automatic recovery of the database. Only in recovery until time with
ora_recut is the relevant control file also recovered. Nor is NSR-ORA in a
position to recognize or correct logical database errors (for instance, if
incorrect files are loaded into the database).
The ORACLE Administrator Guide explains what you can do if you should lose
the control file and/or a number of redolog files. You can also refer to the chapter
“Recovery” of this manual, which describes the restrictions that apply to
automatic recovery for ORACLE Parallel Server (OPS) systems.
In the other two cases (loss of files containing system or user data), NSR-ORA
offers various ways of recovering the data: fully automatic or manual recovery
or restore of a specific database level (recovery until time).
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