Volume Shadow Copy Service (VSS) Information and Troubleshooting VSS issues.

Article:TECH87439  |  Created: 2009-01-17  |  Updated: 2012-10-04  |  Article URL http://www.symantec.com/docs/TECH87439
Article Type
Technical Solution


Environment

Issue



Volume Shadow Copy Service (VSS) Information and Troubleshooting VSS issues.


Solution



By default, VSS is installed with Windows Server 2003 and above. The service is set to a Manual startup type. The service starts if a backup program (the Requestor) can use the VSS Writer or Writers.
 
Use the following items to help troubleshoot an issue may experience with Exchange 2007 VSS backups: 
  • Event log information
  • VSSADMIN commands
  • Diagnostic logging
  • The Exchange Extra tool
Event Log Information
 
The following steps describe the Exchange 2007 backup process that occurs when use VSS together with the corresponding events that are logged. Examine the events that are logged during the backup operation to help determine which component is failing.
 
Step 1: Database Preparation
 
The backup program, also known as the agent, runs a scheduled job.
 
The VSS Requestor in the backup program submits a request to VSS to prepare the selected Exchange storage groups for a snapshot backup.
 
VSS signals the Exchange VSS Writer to prepare for a snapshot backup.
 
The following table lists the series of events that are logged in the Application log for every backup instance that is started.
 
 
 
Step 2: Database Snapshot
 
After the Exchange Writer reports to VSS that the backup preparation is complete, the following actions occur:
 
1 The Exchange Writer freezes the appropriate Exchange databases. In this scenario, Exchange performs the following operations. 
  • Exchange prohibits administrative actions against the particular storage group.
  • Exchange checks volume dependencies for the storage group.
  • Exchange suspends all write operations to the appropriate database files and transaction log files.
Note:- Exchange still allows Read access to the database files and transaction log files.
 
2 When Exchange starts the operation to freeze the Exchange database files and transaction log files, Exchange starts a worker thread to keep track of how long it takes to create the snapshot copy of the database. The copy process is not permitted to take longer than 10 seconds.
 
The whole snapshot copy process may not exceed 70 seconds. This includes all the operations that occur in the "Step 2: Database Snapshot" process. If the whole process exceeds 70 seconds, the worker thread times out. If a time-out occurs, Exchange stops the backup job and unfreezes the Exchange storage groups. Then, Exchange continues typical operations.
 
The following table lists the series of events that are logged in the Application log during the snapshot operation.
 
 
 
Step 3: Shadow Copy Verification
 
The VSS Requestor in the backup program verifies the health of the shadow copy. Then, the program informs Exchange whether the backup was successful. This action signals the completion of the backup operation. The OnBackupComplete() method is used to reset the backupInProgress flag.
 
The following table lists the series of events that are logged in the Application log during the completion of the backup:
 
 
 
When the backup operation exits, the Exchange Writer calls the OnBackupShutdown() method. This method is used to perform operations that are required when a backup program exits after the backup job is finished.
 
If a fatal error has occurred, the OnBackupShutdown() method sets the Exchange Writer status to Failed.
 
The following table lists the series of events that are logged in the Application log during a BackupShutdown event.
 
 
 
The following two function calls occur during a backup failure: 
  • CVssIExchWriter::OnAbort()
  • This method indicates that a shadow copy operation has ended prematurely. The Exchange Writer uses this method to clean up the Exchange Writer and to tell the JET database to thaw (release) the information store. Also, the Exchange Writer uses this method to tell the JET database that the snapshot was stopped.
  • CVssIExchWriter::EcBackupCleanup()
  • If the backup has failed, Exchange uses this method to perform post-backup failure cleanup operations. Exchange uses this method to tell the JET database that the snapshot has failed. Also, Exchange uses this method to tell the information store that the snapshot has failed.
Step 4: Transaction Log Truncation
 
At the end of a successful backup, Exchange performs the following operations:
  • Exchange truncates the transaction log files.
Note:- If not performed an Exchange backup but instead take a snapshot backup of a volume that contains Exchange database files, the backup is handled in the same manner as for an Exchange backup. However, in this scenario, the backup is considered to be a Copy backup, and no transaction log truncation occurs.  
  • Exchange updates the database headers with the appropriate Log Required field information.
  • Exchange clears the backup in progress status.
  • Exchange records the time of the last backup for the appropriate databases.
VSSADMIN Commands
 
Use the VSS administrative command-line tool (VSSADMIN) to obtain information about the Writers and Providers that are registered with VSS.
 
To obtain information about VSS Writers, follow these steps:
 
1 On the Exchange server, click Start, click Run, type cmd, and then click OK.
 
2 At the command prompt, type vssadmin list writers, and then press ENTER. 
Examine the results that are returned to locate the Exchange Writer results. The Exchange Writer should be in a stable state. The following results are returned when the Exchange Writer is in a stable state:
 
Writer name: 'Microsoft Exchange Writer'
 
Writer Id: {76fe1ac4-15f7-4bcd987e-8e1acb462fb7} 
Writer Instance Id: {977637c2-fcdd-463e-b1f8-a9a5d603a2e8} 
State: [1] Stable 
Last error: No error
 
If the State value is anything other than Stable, restart the Microsoft Exchange Information Store service. Results that resemble the following are returned when the Exchange Writer is in a failed state:
 
Writer name: 'Microsoft Exchange Writer' 
Writer Id: {76fe1ac4-15f7-4bcd987e-8e1acb462fb7} 
Writer Instance Id: {977637c2-fcdd-463e-b1f8-a9a5d603a2e8} 
State: [14] Failed 
Last error: Retryable error
 
     3 To obtain information about the registered VSS Providers, type vssadmin list providers at the command prompt. The following results should appear:
 
Provider name: 'Microsoft Software Shadow Copy provider 1.0' 
Provider type: System 
Provider Id: {b5946137-7b9f-4925-af80-51abd60b20d5}
 
Version: 1.0.0.7
 
By default, only the Microsoft Software Shadow Copy provider is listed. However, if a third-party backup program is installed, other providers may be listed.
 
Note:- For more information about the commands that are available, type vssadmin /? at the command prompt.  

 
Diagnostic Logging
 
If suspect that the issue that is caused by an issue with the Exchange Writer, enable diagnostic logging for the Exchange Writer. To do this, follow these steps:
 
NOTE: It is recommended to have Microsoft troubleshoot the writer issue.
1. Start the Exchange Management Shell.
2. Run the following command:
 
get-eventloglevel | where-object {$_.identity -like "*Exchange Writer*"} | set-eventloglevel -level expert
 
3. To verify the logging level for the Exchange Writer, run the following command:
 
get-eventloglevel | where-object {$_.identity -like "*Exchange Writer*"}
 
4. To restore the diagnostic logging level to its default level, run the following command:
 
get-eventloglevel | where-object {$_.identity -like "*Exchange Writer*"} | set-eventloglevel -level Lowest

Acknowledgement:- http://technet.microsoft.com/en-us/library/dd233256.aspx

 




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321181


Article URL http://www.symantec.com/docs/TECH87439


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