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Exchange Server Backup Errors and Circular Logging

When you try to perform a backup, you see this error message in the backup report:

Error: Server\Microsoft Information Store\First Storage Group is not a valid drive, or you do not have access.


There are four possible causes of this:

  1. Your Exchange Server is on a different machine to BackupAssist

  2. Your Exchange Server settings are entered incorrectly

  3. Your backup user identity does not have permissions to backup your Exchange Server

  4. Your Exchange Server is set to Circular Logging, and you are performing a differential or incremental backup


  1. If your Exchange Server is on a different computer to BackupAssist, you need to copy one DLL from your Exchange Server to your backup computer. Please visit;EN-US;275876 for more details.

  2. Please double check your Exchange Server settings - particularly the Storage Groups setting, which must be entered in exactly

  3. Please ensure that your backup user is part of the Administrators group. We recommend using the Administrator domain account to perform backups. Note for SBS users: if you are using the Administrator account but are experiencing this problem, try modifying your Backup User Identity - leave the Domain field blank. This will instruct Windows to use the Default domain, which has been known to fix the problem.

  4. An incremental or differential backup cannot be performed on a storage group with circular logging enabled. Either perform Full backups, or disable circular logging in Exchange. Please visit these URLs? for more details:;en-us;294741 and;en-us;218004

More Information on Circular Logging

An extract from this article:

What is Circular Logging?

In a nutshell circular logging recycles the logs. Exchange relies on transaction or write-ahead logs to store events before they are committed to the database. When 4 logs have been filled up, Circular logging assumes that the first log must have been committed and recycles the logs to save disk space.

Problem with Circular Logging

The fatal flaw with Circular Logging is it restricts disaster recovery. If you allow Circular Logging to over-write the transaction logs then Exchange 2003 can only restore as far as the last backup. When all the logs are available, Exchange 2003 automatically rolls forward the logs and replays the transactions up until the Exchange Store stopped working.

In fact, circular logging prevents Exchange 2003 making differential or incremental backups. So with circular logging in place, you are restricted to normal (full) backup.

  • Unfortunately, differential backups do not purge or truncate the transaction logs, so not only does the differential backup get slightly bigger each day, but the logs are using up more and more disk space until you perform the next full backup.

  • You can check to see if you have circular logging enabled by carrying out the following instructions:

    1. Open the Exchange System Administrator, locate the Servers Icon.

    2. Drill down to the Storage Group where you want to enable circular logging. (Note Storage GROUP not Store...)

    3. Right-click (The Storage Group), and select Properties.

    4. On the General tab, tick Enable circular logging, and then click Yes.

Additionally, this Microsoft article explains circular logging:

An extract from this article:

Circular logging is a very important concept for disaster recovery. When circular logging is turned on, it saves storage by preventing the continuous buildup of transaction-log files on your drive. The downside, of course, is that with circular logging, incremental and differential backups do not occur and, therefore, are not available in case of a crash. Note that circular logging is the default setting in Exchange Server; If you do not want it, you can turn it off through the admin program.

There can also sometimes be small problems when attempting to disable/enable circular logging on your Exchange server, as recorded here:

Ok, I finally have this resolved. I enabled circular logging and restarted exchange. I then disabled circular logging again, and restarted Exchange again. It now works fine. However, I defintely had restarted exchange in the past, as the server has been restarted a few times. I beleive that the circular logging was on by default, but the tick box was never ticked.

Page last modified on October 20, 2005, at 10:03 PM