On Tue, March 5, 2013 10:02, Bob Friesenhahn wrote:

> Rsync does need to read files on the destination filesystem to see if
> they have changed.  If the system has sufficient RAM (and/or L2ARC)
> then files may still be cached from the previous day's run.  In most
> cases only a small subset of the total files are updated (at least on
> my systems) so the caching requirements are small.  Files updated on
> one day are more likely to be the ones updated on subsequent days.

It's also possible to reduce the amount that rsync has to walk the entire
file tree.

Most folks simply do a "rsync --options /my/source/ /the/dest/", but if
you use "zfs diff", and parse/feed the output of that to rsync, then the
amount of thrashing can probably be minimized. Especially useful for file
hierarchies that very many individual files, so you don't have to stat()
every single one.

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