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The Perils of Running Database Repair


The Perils of Running Database Repair

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jswong05
jswong05
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[b]I still do not comprehend a lot of the disk mirror/replication

Using software like doubletake, you can replicate (copy) disk array at data-block level to another environment and keep them in synch. Only the changed data-blocks will be copied.

Jason
http://dbace.us
:-P
kevin77
kevin77
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...we created a test system that took a known database, corrupted it randomly..


How do you manually corrupt the database?



Paul Randal
Paul Randal
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There are test hooks inside SQL Server that the product group can use.

There are plenty of blog posts out there describing how to do it yourself using a hex editor - Google for me and XVI32 and you'll find one.

Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005
M&M
M&M
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...we created a test system that took a known database, corrupted it randomly..


How do you manually corrupt the database?



How to Create a Corrupt SQL Server Database

M&M
jwbrown65
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Thanks Paul. You are extremely gracious with your time on these matters. You helped me a few years ago on a discussion board covering this very topic. We used the REPAIR_ALLOW_DATA_LOSS on a db with more torn pages than an eighth grade math book (ok, not that many). We recovered and restored an old copy of the db as you've suggested here to determine the problem data was outdated. Thanks again.
Chrissy321
Chrissy321
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Will a job with the following fail if corruption exists? Or will the job succeed?

DBCC CHECKDB(N'master') WITH NO_INFOMSGS

I'm suddenly feeling a bit exposed since I am not sure if I would get notified if corruption exists.
chrisfradenburg
chrisfradenburg
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Chrissy321 (6/25/2012)
Will a job with the following fail if corruption exists? Or will the job succeed?

DBCC CHECKDB(N'master') WITH NO_INFOMSGS


The job would fail and report at least some of the errors it encountered. To see all errors you need to use "WITH ALL_ERRORMSGS". That can be combined with NO_INFOMSGS.
Paul Randal
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The job will fail and @@ERROR will be set to the last severity 16 (or higher) message that is output.

Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005
Paul Randal
Paul Randal
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Be careful though because SQL Agent will only capture the first X bytes of the output (unless that changed in recent versions). You may want to go the route of using the undocumented WITH TABLERESULTS and storing the output in a table for later perusal. See here for an example.

Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005
Chrissy321
Chrissy321
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Thanks Paul I will definitely explore that option. I have a monitoring system for failed jobs so it sounds like I would at least be notied that something is amiss. Seems like a good example of maintenance plans being not quite as robust as built or borrowed maintenance scripting.
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