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FAQ entry on partial transfers / binary diffs - fixes #113

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Nick Craig-Wood 2015-08-31 12:47:07 +01:00
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docs/content/faq.md
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@ -73,3 +73,25 @@ Server B> rclone copy /tmp/whatever remote:Backup
The file names you upload from Server A and Server B should be The file names you upload from Server A and Server B should be
different in this case, otherwise some file systems (eg Drive) may different in this case, otherwise some file systems (eg Drive) may
make duplicates. make duplicates.
### Why doesn't rclone support partial transfers / binary diffs like rsync? ###
Rclone stores each file you transfer as a native object on the remote
cloud storage system. This means that you can see the files you
upload as expected using alternative access methods (eg using the
Google Drive web interface). There is a 1:1 mapping between files on
your hard disk and objects created in the cloud storage system.
Cloud storage systems (at least none I've come across yet) don't
support partially uploading an object. You can't take an existing
object, and change some bytes in the middle of it.
It would be possible to make a sync system which stored binary diffs
instead of whole objects like rclone does, but that would break the
1:1 mapping of files on your hard disk to objects in the remote cloud
storage system.
All the cloud storage systems support partial downloads of content, so
it would be possible to make partial downloads work. However to make
this work efficiently this would require storing a significant amount
of metadata, which breaks the desired 1:1 mapping of files to objects.