On 11/3/18 4:35 am, Gordon Messmer wrote:
On Fri, Mar 9, 2018 at 2:57 PM, Stephen Morris <samorris@xxxxxxxxxxxxxxx> wrote:
No, what I was mentioning here is what I have read as standard linux
functionality with copying, when a file is copied, and it doesn't matter
where to, rather than create a 2nd copy of the file, the "copy" is created
as a hard link to the original file, for storage efficiency, and then when
one of the files is updated the hardlink is broken and both files become
physical.
The only process I can think of that works even remotely like that is
rsnapshot (and similar backup systems). In those setups, rsync will
create new files for the first backup. On the second backup, it
creates hard links to all of the files in the set, first, and then
runs rsync to refresh the directory holding the newest backup. When
rsync runs, it does not modify files in place, it creates a new file
and merges data from the local file and data from the remote file in
order to save bandwidth, according to its specialized algorithm. When
it's done, it moves the new file into place, atomically updating the
path in the backup.
As you describe, rsnsapshot uses hard links to conserve disk space and
breaks links when it updates files. My guess is that at some point in
the past, you read about rsnapshot or a similar backup system, and
later remembered their mode of operation as standard functionality.
I can't find the documentation any more, but I have found documentation
on how to use copy the create the target as a hard link or as a soft
link. It is possible I have incorrectly remembered what I had read, or
it is possible over time that the standard copy functionality has
changed and now you have to explicitly specify that you want that
functionality.
regards,
Steve
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