How to determine fault tolerance...

Hi Experts,

Is there a process to determine the level of fault tolerance needed for a particular business operational function?

Thanks!
hermorAsked:
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asian_niceguyCommented:
Depends on the operational function.. what is it?
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DRY_GINCommented:
you can try this, im not sure if it helpful.
it also hase number of references.

http://www.hpl.hp.com/research/papers/vldb2001.pdf


also this

http://www.research.ibm.com/journal/sj/332/ibmsj3302H.pdf
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giltjrCommented:
The level of fault tolerance needed for for a business function is based on the users requirments that need that business function.
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jdietrichCommented:
You need to ask some questions such as:

What is the required recovery time in the event of failure.  All business users will say they need 100% availability, it is always the goal.  But, if the system was down, how long could it be down without a real impact to the business.  This tends to guide the tolerance level built.  Generally speaking you can either use mirroring or raid V.  

Mirroring gives you tolerance for disk failure.  In the event of a disk failure, usually on reboot the raid controller acknowledges that the drive has failed and boots off the mirror.  Then you can replace the original drive during off hours and rebuild the mirror.  So in this case the recovery is almost instantaneous, usually a few (5-10) minutes.

Raid 5 uses parity and spreads the data accross multiple drives.  Usually you have a hot spare (a drive just sitting there waiting).  Upon failure, the controller will rebuild the bad drive on the hot spare based on the info on the other drives in the array.  Depending on the size of the drives, how much data needs to be rebuilt, and the power of the server, this can take 10 minutes to a few hours to rebuild.

This will also depend on the size of the array you are building.  There are quite a few variables involved in making this decision, so be sure to understand the business need and size the server appropriately.  In general, it is easier to expand a raid 5 array than a mirrored one.

Here's a helpful article:
http://www.phptr.com/articles/article.asp?p=20490&rl=1


 
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