Question about Tower of Hanoi Backup Logic

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truwrikodrorowrelupicugojestutroclulachosaswunuhospikigawakijosaswenomaruclojeueclikaspedrubewidebrisubrohutrurifruuagothunugekedrumucisiuobrobrecrupeslapuswosluprothethibakaslechurathikucli
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Posts: 2
Comments: 1

I thought TOH guaranteed restores for 2^(n-1) days (if using daily tapes) or weeks (if using weekly sets), where n= number of tapes/sets in rotation.

I am using a 5 set rotation: A, B, C, D, E.

Week 1: A
Week 2: B
Week 3: A
Week 4: C
etc. (Plenty of charts online explaining this).

I should be able to restore files from any time within 2^5-1 weeks ago, right? That's 16 weeks.

But I've encountered a situation where data is not recoverable even though 16 weeks has not elapsed.

For example, using aformentioned charts as a guide, say a user creates a document in Week 9. It goes on Set A. Then he deletes in in Week 13. Then he decides in Week 22 that he wants to restore it. What set is it on? By my calculations, it has been overwritten (deleted) from sets A, B, and C, and it never was written to D and E. What am I missing?

Thanks

Wed, 02/24/2010 - 22:22
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truwrikodrorowrelupicugojestutroclulachosaswunuhospikigawakijosaswenomaruclojeueclikaspedrubewidebrisubrohutrurifruuagothunugekedrumucisiuobrobrecrupeslapuswosluprothethibakaslechurathikucli
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Posts: 27
Comments: 1940

It's not guaranteed that you can restore data from any of 2^n-1 weeks. There are only n sets and thus only n timepoints to restore from. If the document appeared and then disappeared long ago for a short time, it is already deleted from first sets (because it was long ago) and never appeared on upper sets (because of its short life)

Wed, 02/24/2010 - 23:43