XADM: EDB Event ID 23 Error -1018

• Microsoft Exchange Server, versions 4.0 and 5.0

SYMPTOMS

When you perform an online backup of either the information or directory store, you may see the following entry recorded in the application log:

   Event ID: 23
   Source: EDB
   Type: Error
   Category: Database Page Cache
   Description:  MSExchangeIS ((455)) Direct read found corrupted page
   error -1018 ((1:251563) (0-2295758), 251563 379225672 381322824),
   Please restore the database from a previous backup.

CAUSE

When you perform a transaction with the Jet database, the information store or the directory store writes the transaction to a transaction log file (Edb*.log in Mdbdata or Dsadata). The transaction is then committed to the Jet database from this transaction log. During this process, the Jet engine calculates the page's checksum value to be written, records it in the page header, and then requests that the file system writes the 4-KB page of data to the database on disk. In brief, the file system will take this call and use Windows NT system services to forward this request to the corresponding hardware device driver to actually perform the write. The hardware device driver returns this information to the file system, which then returns it to the Jet engine. If the call is successful, Jet continues.

If you have faulty hardware or hardware that caches requests before it performs the operation, the hardware may return success to calls made to it before it actually performs the physical operation. This is done to improve performance (especially in SCSI controllers and hard drives). When the actual physical operation takes place, however, an error occurs and the data is not written successfully as expected.

When the Microsoft Exchange Server information store or directory store is backed up online, before the 4-KB page is written to tape, a checksum comparison is done. The backup routine makes a request to read a 4-KB page of data from disk. When the request is received, Jet again calculates the checksum value. This checksum from the read operation is then compared with the checksum recorded during the write operation. If there is a mismatch, Jet interprets it as a corrupted page.

RESOLUTION

To resolve the problem, use one of the following methods.

Restore from a Backup

When you encounter the error, the recommended and most reliable way to recover the database is to restore from the last known good backup. However, if the hardware problem still exists, you will continue to have corruption. The Windows NT system log should be reviewed for errors reported by the storage device drivers. These errors should be dealt with and resolved before the database is restored to this server. Another common cause is the use of write-back caching on hard drives. Write-back caching should be turned off on hard disk drives when used with Microsoft Exchange Server (or any transaction log-based relational database system).

IMPORTANT: Only restore the database to the same hardware after the problems have been resolved.

Use Edbutil.exe

As an alternate way to repair the bad page of data, use Edbutil.exe.

IMPORTANT: Make a full offline file backup of the database and log files before running this process. This includes file-level backups of the Exchsrvr\Dsadata and Exchsrvr\Mdbdata folders. This will ensure that there is a way to go back should Edbutil fail.

Edbutil.exe is a low-level Jet database utility that defragments and checks the consistency of the database. There is also a repair option (Edbutil /d /r <dbname>) that attempts to repair bad pages and remove them if the repair is unsuccessful. If a page is removed using the repair option, data loss will occur. A page in a database can contain messages, folders, tables, master indexes, and so forth. There is no way to tell what Edbutil has removed because Jet sees it as raw data. After repair has finished on the Jet database, run Isinteg.exe in fix mode on the same database that Edbutil was run on. Isinteg will clean up any inconsistencies between the pointers from the information store to the actual data in the Jet database. If Isinteg is not run immediately following repair (Edbutil /d /r), corruption may occur in user mailboxes. Users will have messages that cannot be opened, incorrect read/unread counts, and so forth.

Refer to the "Microsoft Exchange Server Administrator's Guide" for more details on the use of Edbutil.exe and Isinteg.exe.