circular logging and Exchange 2013 CU6 DAG

Hi everyone,

I'm implementing the new IPLESS DAG on Exchange 2013 CU6.  

1 - At the end we'll have 3 database copies, the first two locally and the other one at the datacenter.

2 - I've tried to enable circular logging to reduce the number of transactional logs before starting the first seed.    It didn't work.  

3 - Can we enable circular logging on exchange database which has copies as soon as the first copy is done?

Thank you
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Simon Butler (Sembee)ConsultantCommented:
You will be unable to enable a DAG copy with circular logging enabled.
My usual method here would be one of three things.

1. Take a backup of the server immediately before doing the seed. That will flush out the logs.
2. Enable circular logging, then disable it and add the server in to the DAG.
3. Create a new empty database, add to the DAG and then move the mailboxes in to it.

Option 3 is always how I implement a new DAG deployment and it works very well. Trying to add an existing database to a DAG usually results in timeouts, particularly for remote sites.


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quadrumaneAuthor Commented:
Thanks Simon

But as soon as we have 3 database copies or even more the third party  backup option is useless.   As far as I understand the logs will keep growing unless we run a backup to flush out the logs.  Not very practical.  

Thanks also for the third option I'll be using it.
Gareth GudgerSolution ArchitectCommented:
As far as I understand the logs will keep growing unless we run a backup to flush out the logs.  Not very practical.  

Correct. You need an Exchange-aware backup program to back up the database and flush the logs.

But as soon as we have 3 database copies or even more the third party  backup option is useless.

Backup solutions can work with DAGs just fine.
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quadrumaneAuthor Commented:
How many DAG does it take to get rid of the Exchange-aware backup solution?   I can't see why we have to add another layer of backup with so many copies, esspecially when some copies keep older copies of the databases.  

Thanks again
Gareth GudgerSolution ArchitectCommented:
Are you using Lagged Copies? If so, how far out are they?

What is your mailbox and single item retention period?

What is the policy to recover items past that period? For example, recover an email that is 6 months old.

Do you have any compliance requirements that govern how long you should hold email?

Are you archiving email for litigation purposes?

Just a few questions that spring to mind. Will try and think up some more.
quadrumaneAuthor Commented:
Yes I'm using Lagged copies, 1 day and 14 days.  

mailbox and single item retention period is varyiing from 1 year to 6 years depending on the users.  

All incoming and outgoing email are sent to another special mailbox.  Some people are in charge of archiving all those emails.   This is not eDiscovery but we use the public folders so it's easier to find any given email by year, project, senders,. from the Outlook client.    The public folder databases are backed up.  The backup is sent to the datacenter.   We're not using DAG - not yet - for the public folders.

6 years

yes (public folders)

Thanks again
Gareth GudgerSolution ArchitectCommented:
It sounds like you have covered a lot of those bases. The only concern is the database bloat you will get from 6 years of single item recovery. And how large those databases might get.

In a DAG configuration it is recommended the databases stay under 2TB. And preferably I would recommend staying much smaller than that for recoverability time purposes. For example, using ESEUTIL to fix a DB, etc.

I wouldn't recommend manually clearing log files, especially with lagged copies in play.
Simon Butler (Sembee)ConsultantCommented:
If you don't want to run a backup, then you can enable circular logging after the DAG has been setup and all seeding completed. Otherwise you wouldn't be able to run Exchange without backups  - as Microsoft keeps telling us that they do.

What a lot of my clients now do is backup once a month, run with DIR set to 45 days and then retain the backups. In the event of a problem they can go back to the closest month, then use DIR to restore anything deleted.

If you really must keep everything then you need to be using journaling. If you don't need to keep everything, then don't - and get your lawyers to confirm that you don't need to.

quadrumaneAuthor Commented:
Yes.  Only few users are set to 6 years, mostly the partners.   As they're so affraid of deleting anything I've enabled the archive online on another server, other database.  

In order to keep the database under 1 or 2TB many databases have been created.  More databases to manage  but It's also easier to work with when a database goes down and less users are affected.

It's hard to believe that Microsoft is backing up all Exchange servers when they have 16 database copies.  Are you sure there is now way to run DAG?  If not I'll have a backup in place.  

Thanks Gareth
Simon Butler (Sembee)ConsultantCommented:
No, Microsoft are not backing up anything. Certainly not Office365 or They just have multiple copies.
Backups for on prem though are not done for recovery purposes but archiving - hence being able to backup less frequent. Whether to backup or not is a business decision, not an IT decision.

Gareth GudgerSolution ArchitectCommented:
To add to Simon, I believe Office 365 maxes single item retention up to 60 or 90 days (can't remember). To go longer than that they say to just put your mailboxes on hold.
quadrumaneAuthor Commented:
Perhaps they should let us choose.  

Thank you very much for all the answers.  It much more clear.

quadrumaneAuthor Commented:
This guy seems to think it's possible to enable circular logging.  But I'm not sure to understand everything he says.
quadrumaneAuthor Commented:
Gareth GudgerSolution ArchitectCommented:
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