There are three fundamental ways that data on disk becomes corrupted:
- The wrong data is written to the storage media.
- The data is damaged or changed after being stored.
- Data is written to the wrong place on the storage media.
RESOLUTION
=============
A page that reports a -1018 error cannot be repaired; one way or
another it must be expunged from the database. There are three ways
to do this:
- Restore the database from online backup.
A wrong page number or bad checksum is detected during online backup,
and the backup will abort. This means you are assured that the
damaged page did not exist at the time of your last successful backup.
- Defragment the database with NTDSUTIL.
232122 Performing Offline Defragmentation of the Active Directory
Database
http://support.microsoft.com/?id=232122
If the bad page is empty, it will be discarded from the database. The
likelihood that the bad page is empty is greater if the -1018 has
never been seen during normal operation, but only during online
backup or nightly online maintenance.
Offline defragmentation will not finish if a page in use is bad.
Therefore, if defragmentation succeeds, the -1018 will be gone.
- Hard repair the database with NTDSUTIL.
Bad pages will be thrown away by hard repair, and then the database
will try to repair the logical damage left by this hole as best it
can. The success of this strategy is unpredictable, although it works
more often than not and with minimal loss of data. Everything depends
on what was on the page.
IMPORTANT: After running Repair of the database, you should run the
Semantic integrity analysis.
315136 HOW TO: Complete a Semantic Database Analysis for the Active
Directory
http://support.microsoft.com/?id=315136
Repairing a database is usually an inferior strategy compared to
restoring from backup and rolling the database forward. Repair
usually takes longer than restoration and is riskier. Choose repair
only if (1) you do not have a backup, or (2) you cannot roll forward
completely from your backup from some reason.
Tom Ausburne (MSFT)
Windows 2000 Directory Services
This posting is provided "AS IS" with no warranties, and confers no
rights.
