Summary: This blog covers the information about Circular logging & also the steps to Enable Circular Logging in Exchange 2010.
Circular logging allows Microsoft Exchange to overwrite transaction log files after the data that the log files contain has been committed to the database. Circular logging is not recommended in production environments since by enabling it, you reduce drive storage space requirements. However, without a complete set of transaction log files, you cannot recover any data more recent than the last full backup, thus increasing the chances of database corruption. However, you can use Exchange recovery tools such as Eseutil or Stellar Repair for Exchange to repair corrupt EDB file and restore mailbox items.
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How Circular Logging Works?
When circular logging is disabled, every log file goes into the transactional log database, and no limit exists as to how large that database can get. When circular logging is enabled, the transactional log can only grow to one megabyte (1 MB) in size. When this limit has been reached, the first log file is overwritten automatically to keep the transactional log database from growing any larger. The term “circular” arises from the fact that the set of log files starts to “rotate” once the disk space limit is reached, something like a LIFO (last-in, first-out) queue.
Circular logging is a feature of the Joint Engine Technology (JET) database, used by all versions of Exchange Server that can be enabled or disabled by an administrator. In older versions such as Exchange Server 5.5 and earlier, circular logging was enabled by default However, with Exchange 2000 Server and continuing to Exchange 2010 and newer versions, it is disabled by default.
It is suggested that you should not enable circular logging on an Exchange database if you are doing backups as they will be inconsistent. This includes incremental backups as well. If you do however decide to enable it, then it is recommended to take a full backup immediately, after the databases have been mounted and you have disabled it again.
Enabling Circular Logging Exchange 2010
This can be done by using both PowerShell and the Exchange Admin Center (EAC).
Let us start with the EAC. Follow these steps:
- Open the Exchange Admin Center. After logging in, open the databases window.
- In the Mailbox database properties under Maintenance, tick the Enable circular logging checkbox.
- You will immediately be prompted that you would need to dismount and mount the database for the changes to take effect.
To enable circular logging by using PowerShell, you need to open the Exchange Management Shell and use the below command.
Set-MailboxDatabase -Identity “database1” -CircularloggingEnabled:$true
Alternatively, if you want to do it for all the databases, you can use the below command.
Get-MailboxDatabase | Set-MailboxDatabase CircularloggingEnabled:$true
After the databases have been dismounted and remounted, it is strongly suggested to perform a full backup of your Exchange database.
Let’s now look at a scenario where the Exchange backups have not been taking place and the volume where the database is stored is filling up. Once you hit that specific backpressure threshold, then you risk the fact that the Exchange Databases will not mount.
If you are in this situation, do not just jump and enable circular logging so you can get rid of the log files to reclaim the space they have used.
Firstly, make a copy of the log and database directory, if you need to restore the database from a backup and replay the logs.
If you do not have them, you can end up with data loss. You must try recovering your Exchange database from backup.
If you are running a large environment and want to make use of circular logging in the long run, it is advised to have three copies of the data if you want to go backup-less with Exchange Native Data protection.
The next thing is, if you are running a Database Availability Group and you are on an Exchange version higher than SP1 for Exchange 2010, then you no longer need to dismount and mount the Exchange stores for this to take effect.
You do not need to restart the Information Store Service. It takes a few seconds/minutes to perform this.
Lastly, if you have had a problem and enabled circular logging in Exchange 2010 but the Exchange database wont mount, then you need to look at a third party Exchange Recovery tool such as Stellar Repair for Exchange to repair the corrupt EDB file without the need for the log files.
The software can repair large .EDB files as well as multiple files, simultaneously. You can even open the offline .EDB file with the tool and just extract the data to another live database or Office 365 tenant, or even to a .PST file. The software supports all Exchange server versions such as 2019, 2016, 2013, 2010, 2007, 2003 , 2000 & 5.5