Alot.

How much depends on how you're TSM server is configured, but for a large 
TSM database(+60GB) I would not recommend using serialized database 
mirroring.

We have a customer running a 220GB TSM database. Using sequential writes 
wouldnt be an option as the performance loss would be to big.

Using sequential mode means TSM will 1st write to one of the copies and 
after that write to the other copy(if the 1st write was succesful). This 
means every I/O you make to the TSM database in reality is 2 IO:s the TSM 
server will have to perform each time. Considering the amount of I/O the 
TSM server performs, the performance hit will be large.

The security risk is mainly in a scenario were TSM writes to both of the 
db volumes and crashes at the same time. This could result in a partial 
write = database restore. To avoid this security issue when using parallel 
writes, enable pageshadowing with "dbpageshadow yes" and "dbpageshadowfile 
FILENAME". The pageshadowfile should preferable be placed on separate 
disks from the TSM database volumes.

Hope this help

Best Regards

Daniel Sparrman
-----------------------------------
Daniel Sparrman
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Exist i Stockholm AB
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183 62 TÄBY
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Roger Deschner <rogerd AT UIC DOT EDU> 
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2005-07-30 03:53
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Subject
mirrorwritedb parallel - tried it?






I'm fighting performance problems with a big TSM database, and I was
curious if anybody has experience with how much mirrorwritedb parallel
could help.

More importantly, what are the risks?

Roger Deschner      University of Illinois at Chicago     rogerd AT uic DOT edu
============ "In theory, theory and practice are the same, =============
========= but in practice, theory and practice are different." =========