Will this break mirroring?

Question

Will this break mirroring?

Adam Bean

One Orange Chip

Points: 26631
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March 14, 2008 at 1:49 pm

#128306

Hey all,
Say my mirror is suspended and during this suspend time the principal has seen a MASS amount of change (tlog grew ~20gb on the principal). When I resume mirroring, I'm assuming that the mirror will be synch'd via the principal's TLOG ... Well, what happens when I run a TLOG backup on the principal? Will the mirror be unable to recovery after a TLOG backup occurs?
Thanks

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Lynn Pettis SSC Guru Points: 442467 More actions · Answer 1

I'd be curious about this as well. I'll give you my swag, the transaction log backup will work, but the commited transaction may not get deleted. Sort of like what happens with replication, unitl the data is actually replicated, the transaction log won't get truncated.

Just a guess now, so don't take it as gospel. Again, I would be curious, as we are looking at implementing mirrioring for DR purposes.

😎

Adam Bean One Orange Chip Points: 26631 More actions · Answer 2

Same here ... I think I'm gonna let my TLOG backup run and see what happens when I resume the mirror out of sheer curiosity ...

Lynn Pettis SSC Guru Points: 442467 More actions · Answer 3

Be sure to report back your findings. I'm sure I am not the only one interested.

😎

Adam Bean One Orange Chip Points: 26631 More actions · Answer 4

Think I found my answer ...

http://www.microsoft.com/technet/prodtechnol/sql/2005/dbmirror.mspx

Database mirroring will not be able to initialize if transaction log records have been truncated from the log by log backups. Therefore you must restore those transaction log backups in sequence to the intended mirror database with norecovery before database mirroring will be able to initialize.

Figured as much, but was curious nonetheless ...

Lynn Pettis SSC Guru Points: 442467 More actions · Answer 5

Okay, so it isn't similiar to replication. Good thing to know.

Thanks

😎

Balmukund SSCertifiable Points: 6648 More actions · Answer 6

Adam Bean (3/14/2008)
Think I found my answer ...
http://www.microsoft.com/technet/prodtechnol/sql/2005/dbmirror.mspx
Database mirroring will not be able to initialize if transaction log records have been truncated from the log by log backups. Therefore you must restore those transaction log backups in sequence to the intended mirror database with norecovery before database mirroring will be able to initialize.
Figured as much, but was curious nonetheless ...

I guess the link which was posted here is for setting up the mirroring. Once the mirroing is setup, we should be able to take log backup from primary.

If you try to do below

backup log test with truncate_only

Msg 3048, Level 16, State 1, Line 1

BACKUP LOG WITH TRUNCATE_ONLY cannot operate on database 'test' because it is configured for database mirroring.

Msg 3013, Level 16, State 1, Line 1

BACKUP LOG is terminating abnormally.

Adam Bean One Orange Chip Points: 26631 More actions · Answer 7

Well, I'm happy to report that while mirroring is suspended, a TLOG backup does NOT remove committed data that has not yet been applied to the mirror. I was able to turn on mirroring without any issues.