[Box Backup] Deleting old snapshots

Ben Summers boxbackup at fluffy.co.uk
Thu Apr 7 21:12:09 BST 2005

On 7 Apr 2005, at 16:29, Richard Wallace wrote:

> Ben Summers wrote:
> <snip/>
>> Currently, directories contain chains of deltas. If a client decides 
>> to upload a patch instead of a new file, that patch is applied to the 
>> relevant file, and that generated full version is stored as the 
>> latest version in the directory. Then, the patch is reversed (so it's 
>> a patch from the latest version to the previous version) and the 
>> previous (full) version is replaced with this patch.
> Ok, this is pretty much the same way that rdiff-backup works too.  The 
> only thing I'm uncertain about is how the server can apply the deltas 
> and reverse them when the deltas and the full version are both 
> encrypted.  The server doesn't have to decrypt them to do it, does it?

Of course not.

The files aren't encrypted in all one go, they're encrypted in lots of 
independent blocks. Essentially all the server does is rearrange and 
combine blocks. This allows everything to remain encrypted, but still 
yields most of the performance and bandwidth reduction that unencrypted 
rsync provides.


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