I work in an environment that used rsync heavily for system mirroring.
We've noticed that some of our machines are reaching their IO limit during
the bi-hourly rsync run. To my understanding, rsync transfers only the
files that have changed, but must read every file from the disk to make that
determination. Is there a way to improve this performance? Perhaps a way
to cache a list of changed files to give to rsync on the bi-hourly run? It
believe I heard about a kernel option for this which is used in HA
clustering. Can someone offer any guidance?

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