%1 (%2) %3An attempt to determine the minimum I/O block size for the volume “%4” containing “%5” failed with system error %7: “%8”. The operation will fail with error %6.

Product: Exchange
Event ID: 491
Source: ESE
Version: 8.0
Message: %1 (%2) %3An attempt to determine the minimum I/O block size for the volume “%4” containing “%5” failed with system error %7: “%8”. The operation will fail with error %6.

This Warning event indicates that an unexpected error was encountered while trying to use the volume specified in the message. Specifically, an error occurred when an attempt to determine the I/O block size for the volume failed.

The cause depends on the error listed at the end of the Description section of the event. The most frequent causes are listed below.

  • Error -1032 = 0xfffffbf8 = 4294966264 = Jet_errFileAccessDenied = Cannot access file. The file is locked or in use. Another process has locked the file. Antivirus software may mistakenly quarantine a file, or a backup process may temporarily deny access. A flat file backup system or antivirus software may be running against the database, check file directories, or the M drive. This error can also occur if the permissions on the folder that contain the files for the Exchange stores are not sufficient for the stores to function properly.

  • Error -1022 = 0xfffffc02 = 4294966274 = Jet_errDiskIO = disk I/O error. The -1022 error is a generic error that appears whenever a disk I/O problem prevents Exchange from gaining access to a requested page in the database or to a check file. A disk or controller failure may have occurred and access to the entire drive has been lost, sometimes temporarily. The physical drive may no longer be accessible or have an incorrect file system, such as accidentally specifying the transaction log files path to the CD-ROM drive. Check the System log for I/O or drive errors near the time of the 491 event. This issue may occur because the path for the check file (such as E00.chk) is not correct, which may be caused by a drive failure.

User Action

To resolve this warning, do one or more of the following:

  • For error -1032, change the folders that contain the Exchange store files to default permissions. Configure the flat file backup and antivirus software to not scan the Exchange store subdirectories or the M drive. Use Exchange-aware online backup and antivirus software.

  • For error -1022, ensure that the drive for the Exchange store files is accessible and that the path for the Exchange store files is specified correctly. If it is, run chkdsk /f /r. If Chkdsk does not resolve the issue, examine the permissions on the Exchsrvr folder structure. Ensure that System has full control of theC:\Program Files\Microsoft\Exchange Server folder, where C:\ is the directory to which you installed Exchange 2007, and all subfolders on each partition that contains Exchange data. If you still cannot mount the databases, troubleshoot any Windows NT file-level antivirus software running on the Exchange server. Check the System log for I/O or drive errors near the time of the 490 Event. Check and correct the path for the check file (such as E00.chk).

  • For information about ESE error codes other than the ones explained in this topic, see the following Microsoft Knowledge Base articles:

  • After correcting the root cause, if the database is inconsistent, restore from online backup. If there is no valid backup, you can restore the database to consistency using the hard repair (/p) functionality of the Eseutil utility, run isinteg -fix until all fixes are removed, mount the database, and then ExMerge to a new, blank database. Before doing this, you should always back up all information store files in a storage group (*.log files, *.edb files and *.stm files).

If you are not already doing so, consider running the tools that Microsoft Exchange offers to help administrators analyze and troubleshoot their Exchange environment. These tools can help you make sure that your configuration is in line with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. Go to the Toolbox node of the Exchange Management Console to run these tools now. For more information about these tools, see Toolbox in the Exchange Server 2007 Help.


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