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Exchange 2007 Transaction Logs

Posted on 2007-11-18
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Last Modified: 2010-03-06
Similar to another post I have read on here (but doesn't answer my specific question) we are experiencing a large amount of transaction logs building up.
My colleague who deals with backup is having some issues with Exchange backing up properly at the moment and as a result i suspect that it is because of this reason that the transaction logs are not clearing, and are already up to 32Gb (on a 50GB) disk.
Is it possibly to delete logs that are more than a couple of days old?
Other than resolving the backup issue, is there anything else I can do to keep disaster at bay in the meantime?
Cheers,
P.
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Question by:prospatho
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by:mass2612
ID: 20310991
Hi,

You are correct. The transaction logs will be purged once a full backup is ciompleted. I would not delete the logs. Have you tried using NTBackup to backup the Exchange Information Store? Sort out the backup ASAP. If you can't and are getting really low on space I would stop the Exchange Information Store (this will cause an outage for your users). Backup the Exchange EDB files manually by copying if you have to. Then you can move some of the log files to a temp location and then restart the Information store and remount the databases.

Currently if your backup is not working then your transaction logs are your only option to use to recover data in the event of a failure.

You could enable circular logging but I would not recommend it but it is an option. Doing that would be considered a bad idea from MS supports point of view.
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by:Sembee
ID: 20315229
Just to echo what has been said above - run a backup of NTBACKUP. DO NOT delete the transaction logs manually - that will cause problems with Exchange.

Simon.
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by:prospatho
ID: 20318719
My colleagues are insistent that deleting transaction logs with archive bit cleared  - manually - is not a problem.
Can you confirm or refute this?
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by:mass2612
ID: 20318819
Deleting the transaction logs in not something you should do. If you must you can move them but should never to delete them manually. Get the backup working! If you don't have a current known good backup in the event of a failure these log files are the only way you are going to be able to get your data back past the date of the last known good backup.

For example if your backup has not succeeded since the 31st October and you have a database corruption, hardware failure etc and need to restore Exchange using the backup from the 31st all your e-mail will be gone between the 31st and now if you don't have the transaction logs. If you do have the logs then you should be able to replay the logs to the restored database from the 31st and retireve the data up to the current point in time. That's why they exist.

http://support.microsoft.com/kb/240145

"Copy all the transaction log files that you want to remove to a different location before you permanently remove them from the transaction log hard disk. Do not permanently delete the transaction log files until you have successfully completed a full online backup of all the databases in the storage group."

http://technet.microsoft.com/en-us/library/bb219028.aspx
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by:Sembee
ID: 20319042
The archive bit has nothing to do with the how Exchange manages the transaction logs. Remember Exchange is not backed up in the regular way. It isn't a file system, it is a database. You don't backup the transaction log files at all, when the database has been backed up the logs are marked as committed and flushed. If you have logs that are dated before the last full backup then you could delete those manually, after ensuring that the backup is working correctly and it was a Full backup, not a copy or incremental. However what you should do is investigate why the logs are not being flushed.

To put it bluntly, your colleagues are wrong.
They may have got away with deleting the logs manually in the past, but that does not mean they always will or that it was the right thing to do.

Simon.
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Author Comment

by:prospatho
ID: 20337475
Simon,
Thanks so much for your answers, and have taken note!
However we still have a problem in that a full backup was otherwise successful a couple of days ago.
But It has not flushed the logs.
we are still looking into why (and have read the EE article on this too).

My question at the moment is, for the time being, in the event that I'm unable to have an ntbackup perfomed (I do not have control over backups unfortunately) , is it necessary to stop the databases in the store in order to copy logs out that have had archive bit cleared. (NB I have noted that you do not recommend manually - however if I can take no alternative action other than to manully delete logs..in order to continue migrations - unitl the backupexec problem is resolved..)

Thanks, P.

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by:Sembee
ID: 20338822
Ignore the archive bit. That has nothing to do with this. Exchange is not a file system, it is a database.

Bottom line - you cannot move the transaction logs to another location. That is just as bad as deleting them. Exchange knows where they should be and will be expecting them to be there.
Does Exchange report that it has had a successful backup?
As you are using Backup Exec, have you tried to run a backup of Exchange using ntbackup? If you have access to the server then you can run ntbackup.

Simon.
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Author Comment

by:prospatho
ID: 20347685
Hi Simon,
Backup Exec is used for backup. However I have also tried to use Ntbackup.
No errors are reported in either BE or ntbackup - however the logs are not being cleared..
I am using an account with enterprise admin rights on the Exchange server..
Logs are building up - I tried to move the logs last night to a larger drive to avert a disaster, but the move failed (Call cancelled)
What to try next?
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by:mass2612
ID: 20347883
Can you confirm via ESM that the backups are working. You do this via the ESM > Expand your Org > Expand your Admin Unit > Expand Servers > Expand the Information store and then right click the Database > Properties > Database tab. There is an option there that states if the backup was successfull.
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by:Sembee
ID: 20347917
mass2612 - That is the place on Exchange 2003, however on Exchange 2007 it is slightly different.

EMC, Server Config, Right click on the information store and choose Properties. The first tab has the backup status.

However checking whether Exchange thinks the backups are working correctly is important. The Call cancelled is worrying - that would tend to indicate something may be wrong with the file system or blocking the files. Have you checked that AV software is not scanning that directory?

Simon.
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by:mass2612
ID: 20347922
Sorry the Ex 2007 steps are EMC > Server Config > Mailbox > Select your server > Expand your storage group > Right click Mailbox Database > Properties > General > Last Full Backup field. Please note the logs will only be cleared if a normal full backup is run. VSS won't do it.
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Author Comment

by:prospatho
ID: 20348242
Thanks for your comments - much appreciated!
I have checked the backup status on these databases and ststus is as assumed -done today.
There is No AV software scanning in hte background either.
I have a theory which I'm in the middle of testing at present and will keep you posted...
If you have any further thoughts at this stage, please let me know..
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Author Comment

by:prospatho
ID: 20354891
I have now resovled the problem and the transaction logs are now cleraing.
I had set up LCR on the server and had previously disabled it (as i was having other problems that I thought might have been related to LCR).
As soon as I re-enabled LCR (after having to disable and re-enable it) on the storage groups, the transaction logs promptly cleared.
I haven't seen this documented anywhere.
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mass2612 earned 500 total points
ID: 20355266
Thanks for the update. This is just for everyone's future reference. When LCR is enabled the truncation of the logs by Exchange aware backups means that the log cannot be deleted until the LCR registers the log as being successfully copied to the LCR location.

Exchange Backups and LCR
http://technet.microsoft.com/en-us/library/aa998195.aspx
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Author Comment

by:prospatho
ID: 20355843
Thanks Guys!
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