Then I found Vembu Storegrid: http://www.vembu.com/
This product states that it uses the rsync algorithm to transmit file changes
over the wire. This is reasonable because they have a version for ISPs where
obviously backup of files over the Internet can benefit from using the rsync
algorithm. They call their version "Intelli-Data".
However, perusing the forum, where a more detailed description is available
in response to queries, it appears that they actually do store only the delta
diffs of the file as well as the original file, with version information and
date/time.
This means the product is actually similar to rdiff-backup in its backup
method.
This is important because I emailed the company asking them about large file
support and they explicitly stated that they have tested it with files of up
to 40GB. They didn't mention that it was a form of rdiff-backup, only that it
used the rsync algorithm.
The product costs only $30 per PC, with an additional $20 for an open file
plugin. They also have a free version which works on a maximum of 3 networked
PCs (the product is network aware and detects more than 3).
The product can be run in server mode, client mode, or both, and can be run
as an application or a service under Windows. Versions are available for
Windows, Linux, FreeBSD, and Mac OS X.
Just a heads up for anyone looking for an rdiff-type backup for Windows that
can handle large files.
I'm currently attempting to test it on large video files. However, it seems
that re-rendering the file (perhaps after deleting some frames or whatever)
appears to cause the product to treat the file as requiring a complete
backup.
This raises a question: if you delete a section of a file, I would expect the
rsync algorithm to still be able to detect and transmit only the changed
bytes, due to the "rolling" nature of the checksum. Surely rsync doesn't
depend on the specific location of the bytes in the file. Why would
re-rendering a video file onto itself change so much of the file that the
rsync algorithm would detect all the bytes as changed?
Or am I completely wrong about how rsync works?
Any ideas?
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