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How do cloud storage providers (such as Dropbox, Apple iCloud, Evernote etc.) provide redundant data storage, whilst simultaneously routing my query to a server with a corresponding copy of my data.

Say for example, I have a document "CV.docx", which I store in Dropbox. Dropbox needs to keep a redundant copy of this file (to allow for hardware failure, loss of connectivity etc.), say they store this on Server 1 & Server 2. When I later make request to download this file, how does Dropbox know which servers are storing my files, and route my request to Server 1 or 2, as opposed to Server 500.

Is this pairing of storage locations to documents stored in a central database that my request has to jump through? If so wouldn't this present a single point of failure? I am guessing that this database is replicated, but does this scale to millions of users?

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closed as not a real question by Michael Hampton, mrdenny Aug 11 '12 at 4:04

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

Cloud can many different things... in my world... cloud means "automated multi-tenancy". For some people cloud means geographic redundancy.

So in the world of file storage, it depends on the provider. Apple is probably replicating data into two or more places using some kind of incremental storage synchronization. They're also probably breaking this down into a front end, and a back end, and coming up with some clever ways to efficiently store the data.

I think the best answer I can give you, is that we here can't really authoritatively answer about what somebody else is doing. You will have to do your own research.

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