[Bug 8615] New: feature request 'update by reference'

[samba-bugs at samba.org]

https://bugzilla.samba.org/show_bug.cgi?id=8615

           Summary: feature request 'update by reference'
           Product: rsync
           Version: 3.0.9
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: core
        AssignedTo: wayned at samba.org
        ReportedBy: info at ecsystems.nl
         QAContact: rsync-qa at samba.org


This is a new feature request for rsync.
I call it a 'update by reference' option.

What is it suppose to do?
Update(create) a target file by using a (server)local file that is similar to
the target being updated.

Scenario:
On a rsync server,
/Folder1/huge_file_1

On a rsync client,
/FolderLocal/huge_file_2

Commandline example:
rsync -rvt --inplace /FolderLocal/huge_file_2
root at 127.0.0.1::Folder1/huge_file_2 --byref Folder1/huge_file_1

The file 'huge_file_2' will be created on the Server as '/Folder1/huge_file_2'
but the actual Delta is taken from the difference between
'/FolderLocal/huge_file_2' and '/Folder1/huge_file_1' (the reference file)

Argumentation:
A remote site holds large backup files which are created far away each day,
these backup files do not differ alot from day to day but have to be made due
to a backup policy.

Each day backup is then a new file which a rsync remote site does not know
anything about and thus the entire backup file needs to be send across, this is
wasting alot of bandwidth and alot of transfer time.

However the remote rsync site does know about previous backup files that might
contain alot of similar data blocks.

If we could tell the remote rsync site(server) to 'create' the new backup file
but reference the Delta on another file we might save alot of bandwidth and
time.

Personally I've done and still doing this manually with DVD images by copying a
DVD image that is most similar to the one being rsynced to the new named target
and then 'delta overwrite' it with the real image file, not perfect but it does
save me about 35% bandwidth and 45% time. These are just 4-5gb files, backup
files run into the hundreds of gb's so a 'quick copy' like this dvd example is
not an option.

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