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Circular Logging in SBS 2011

Posted on 2012-04-06
Medium Priority
Last Modified: 2012-12-21
Should circular logging be turned on in Exchange 2010 on a SBS 2011 box?

I know it was on by default when we first installed the server.

Now it is off - maybe a MS update turned it off - it was on and we did not change it.

We have had issues with the number of log files growing huge (currently the folder that houses the log files is 5GB - 5,728 files).

We paid MS for a support incident - very expensive and got someone who I don't think was all that experienced - he said in an SBS 2011 environment it should be enabled.

Very confused about this as MS states this in the their help file...

"You can configure Exchange to save disk space by enabling circular logging. Circular logging allows Exchange to overwrite transaction log files after the data that the log files contain is committed to the database. However, if circular logging is enabled, you can recover data only up until the last full backup. For example, you can enable circular logging when using Exchange native data protection, in which you don't make backups. To prevent log buildup, you need to enable circular logging.

In the standard transaction logging used by Exchange 2010, each database transaction is written to a log file and then to the database. When a log file reaches one MB in size, it's renamed, and a new log file is created. Over time, this results in a set of log files. If Exchange stops unexpectedly, you can recover the transactions by replaying the data from these log files into the database. Circular logging overwrites and reuses the first log file after the data it contains has been written to the database.

In Exchange 2010, circular logging is disabled by default. By enabling it, you reduce drive storage space requirements. However, without a complete set of transaction log files, you can't recover any data more recent than the last full backup. In a normal production environment, circular logging isn't recommended.

For information about how to enable and disable circular logging, see Configure Mailbox Database Properties."

We are getting good backups with the SBS built-in backup program.

Any help would be appreciated.  Thank you.
Question by:lcstech1

Expert Comment

ID: 37818282
I prefer not to use circular logging, rather incremental backups daily as they will flush the logs after backup.  It's fine to use, but as they stated, if your server crashes, email will be lost with circular on.
LVL 74

Accepted Solution

Glen Knight earned 1000 total points
ID: 37818417
Circular logging is enabled by default in SBS2011.  Some will disagree with me but I will always do this on an SBS box.

My reasoning, the disks that you store the database on are normally the same ones you store the logs on (in SBS).  So if the disks fail you've lost the database and the logs.  So you will still be in a position where you can only recover to your last backup.

In this situation the logs provide you with little security and are therefore of no use.
LVL 70

Assisted Solution

KCTS earned 1000 total points
ID: 37818792
If circular logging is enabled then your ability to recover exhange to the point just before a problem is lost.  You can only recover to the point when the last backup was done. Depending on your system, what you are using exchnage for, and the importance (to you), of your emails this may (or may not), be an issue.

With circular logging disabled, then you can recover to the point of failure by replaying the trasaction logs, of course as has been said, this is only true if the logs are not lost as well (which is why a seperate disk is recommended for the log files), this is vital to many users, in this situation the transaction logs are only truncated when a backup is run.

You need to decide which is the best option for your situation.
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LVL 74

Expert Comment

by:Glen Knight
ID: 37818815
I prefer to invest the money in making sure my hardware is redundant enough that the diss shouldn't completely fail.

On an SBS server the budget to do this over multiple RAID volumes is normally limited.  Therefore space is ov a premium which is why circular logging is used.

If you have a default install with Exchange Database & Logs on the same drive I see no issue with this.

A lot of small businesses will use the outlook local cache as part of their backup plans.

Author Comment

ID: 37819191
I am leaning towards turning it on as we had the log files previously grow to over 750GB in size - we had not been getting good backups... (this is when we hired a MS tech to remote in and he basically crashed the server and put the database in a dirty shutdown state).

Is it true that the log files are only removed upon completion of good backups? - or should they have been removed as they were committed to the database file?

BTW - thank you all for comments and insight.
LVL 74

Expert Comment

by:Glen Knight
ID: 37819199
The log file is a record of what has been applied to the database.

So when you backup the database using the full Method of an Exchange aware backup product the logs are flushed.

Author Comment

ID: 37819248
Yes, but I understand that some log files may be uncomitted to the database - and therefore not truly written to the database - is that correct?

Also, we are using the backup program built-in to SBS 2011 (scheduled to backup to daily at 10:00pm) - I am not sure how often it does a full backup and how often it is an incremental backup and whether or not it flushes the logs files during the incremental backups?
LVL 74

Expert Comment

by:Glen Knight
ID: 37819281
No.  The data is committed to the database.  The logs are just a record of this.

Incremental is a waste of time.  Full backups should be performed of the exchange database every time it is backed up.

Author Comment

ID: 37819423
Ok, I am still not sure what the best setting is on SBS 2011 - can someone else please comment on this?

Thank you.

Expert Comment

ID: 38713726
To do Full backups:  In Windows Server Backup (not SBS console) Clik on Backup Schedule and you need to select "Custom" not "Full Server", on the next screen click "add items" and CAREFULLY select bare metal, and all drives you want to backup.  On this same screen, click on "Advanced Settings", select "VSS Settings" Tab and select VSS Full Backup.

Note:  The above setting is not the default in SBS 2011 because a full backup is not necessary as circular logging is enabled by default.

In Windows Server Backup you can also click on "Configure Performance Settings" in the right actions pane and select Normal or Faster Backup.  Normal is Full backups and Faster is Incremental backups using shadow copies that may slow down your server.

Note:  The above setting is not the default in SBS 2011 because "Normal" will take up more backup drive space and the backup process will be slower.

Windows backup is very limited, but reliable.  If you want more control, one of the best and least expensive SERVER backup programs is Macrium Reflect Server.  I do not recommend Acronis even though it has more features then Macrium.  Acronis software has gone down hill in recent years. It used to be great, but it's now  buggy, bloated, unreliable, complicated and expensive.

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