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Backups


Backups

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Lynn Pettis
Lynn Pettis
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SQL Dude-467553 (4/30/2010)
I think this question really makes me think. I thought the log backup chain was broken after a full backup based on this I read on MSDN

"If a log backup becomes missing or damaged, start a new log chain by creating a full or differential database backup and then backing up the transaction log to start a new log chain. We recommend that you retain transaction logs backups that come before a missing log backup, in case you ever want to restore the database to a point in time within those backups. For information about how to help protect your backups, see Security Considerations for Backup and Restore (SQL Server)."


If a t-log backup becomes damaged or missing, yes, you need to start a new log chain by performing a full or differential backup. The key here is that the full and differential backups themselves don't BREAK a log chain.

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Lynn Pettis

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Nice Marmot
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LOL This is just like one of the certification questions. Nice one, Lynn.
Lynn Pettis
Lynn Pettis
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Nice Marmot (4/30/2010)
LOL This is just like one of the certification questions. Nice one, Lynn.


Thanks. I guess I'm glad I haven't taken any of the certification tests.

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Lynn Pettis

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SQLRNNR
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Steve Jones - Editor (4/30/2010)
CirquedeSQLeil (4/29/2010)
Thanks Lynn.
The part that gets me with these questions is if the hardware failure was enough to corrupt the database and the full backup - it would seem to me that you would be unable to perform a tail log backup. After all the failure had to be severe enough that it was able to corrupt files on different drives / luns. Thus I always have to step back and think a little more about it. It must not have been too severe of a hardware failure because the database was able to be brought back online.


Not necessarily, I think you're caught up in the high end systems. Lots of people have logs/data/bus on one set of disks, often R5. Possible that someone could scribble on a backup and data file and not necessarily the log file. Or enough of the data file to make it necessary to restore.


Good point.



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Nice Marmot (4/30/2010)
LOL This is just like one of the certification questions. Nice one, Lynn.


I imagine there are plenty of these types of questions on the current exams. There were plenty for the older versions.



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Richard M.
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Nice one Lynn. Very good question... and something learned Smile

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Tom Garth
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I did just take the cert exam, and I'm glad this one wasn't on it. I too thought that a full backup broke the log chain.

Thanks for a good and educational question.

Tom Garth
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Shriniket
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In the recovery steps use of "latest differential backup" is misleading; I know it does say Tuesday @4pm but shouldn't the "latest differential" be Wednesday @8am? What would be accurate is if it said "latest differential based on Mondays Full Backup"
Lynn Pettis
Lynn Pettis
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Shriniket (4/30/2010)
In the recovery steps use of "latest differential backup" is misleading; I know it does say Tuesday @4pm but shouldn't the "latest differential" be Wednesday @8am? What would be accurate is if it said "latest differential based on Mondays Full Backup"


This one has come up a couple of times, so I'll address it. First, sorry if I didn't spell everything out in explicit detail. With that said, it is a matter of interpration based on context. In the context of the scenario, the restore is starting with the Monday night full backup, what is the latest differential backup? Answer, not the one taken at 8:00 AM Wednesday.

If I tell my co-worker I am restoring the Monday night full backup, tell me what the lastest differential backup is while I get this started. I would expect him (or her) to look up the correct file with my having to specify "based on the Mondays Full Backup."

Now, if this individual is a new junior DBA, and wasn't sure, I'd expect them to ask. I'd also be making sure that they learn about backup/restores as they may find themselves having to do it when I'm not available to assist.

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Lynn Pettis

For better assistance in answering your questions, click here
For tips to get better help with Performance Problems, click here
For Running Totals and its variations, click here or when working with partitioned tables
For more about Tally Tables, click here
For more about Cross Tabs and Pivots, click here and here
Managing Transaction Logs

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Shriniket
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Lynn Pettis (4/30/2010)... With that said, it is a matter of interpration based on context. ...


I think that says it, maybe this could have been a trick question where latest differential did mean Wed 8am which would question one's knowledge of how back ups work ... any how ... please don't apologize, very good question and makes for interesting conversation :-)
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