On 09/10/2015 01:40 PM, Paul Smith wrote:
Thanks, Rick, for your reply. The idea of a cloning application with differential / incremental backup is not mine, but inspired on what is written at the clonezilla site: "Differential/incremental backup is not implemented yet."
It's important for that conversation to define what an incremental backup is, because it can mean different things.
For instance, some users might want to send only the changed blocks of a disk over a network to a remote system. In order to do that, you need a process on each side of the network which can read the disk and its remote image, communicate about each block in turn, and send/store the blocks which are changed. rsync is an implementation of that strategy. It'll save bandwidth when only a portion of the blocks have changed, but is often slower than just sending the entire file over fast networks.
Right now, clonezilla uses one of a handful of filesystem dumping tools for efficient dumping of some filesystems, "dd" for other filesystems, and storage on dumb destinations like smb, nfs, or ssh(sftp?). Supporting incremental copies means adding rsync-like capabilities to all of the individual tools that clonezilla uses, or integrating all of their fileystem-reading code into clonezilla itself and implementing the incremental copy once. Either way, that's probably more engineering than all of the work that has gone into clonezilla, combined.
On the other hand, some users might not care about the network bandwidth at all, but they might want the block differences themselves recorded in a separate file on the file server, so that they can have multiple images, with the possibility to restore any one of them for a point-in-time recovery.
That's less work than the previous option, but it's still not simple. Unless someone with the need to do that, specifically, steps up to do the work or pay for it, I wouldn't expect such a feature to ever be implemented.
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