Block check latency

When implementing a backup system we may need the client to ask the server if it already has a certain block. There are several ways we can implement this in order to reduce latency impacts; Option 1 Client sends block hash to server Server replies Y/N High latency impact Option 2 Server sends client a list of all block hashes on server Client is then free to stream in new blocks as fast as it can No latency impact Sensitive data release?
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Design of backup software

This article covers the design of an ideal file-based backup solution. DESIRED PROPERTIES Untrusted server Incremental forever METHOD Split file into blocks using rsync algorithm / deterministic reparse points This makes it very likely that a 1B addition in the middle of the file won’t cause an entire reupload of the following sections Use a block interval that is quite large (e.g. 100KB) to minimise size of metadata
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Introduction to encrypted, incremental backup

There are a few approaches to encrypted incremental backup assuming the constraints are (1) we don’t trust the remote storage provider to snoop through our data, so it must be encrypted client-side; and (2) bandwidth is expensive, we want to minimise data sent to the remote storage provider - that includes only ever sending the changes to our data. Take duplicity[1] for instance. In order to work with untrusted remote storage sites, all data is encrypted and the encryption key is never exposed to the remote storage provider.
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