rsync --inplace dead slow

[Roland @web.de]

hello,

i observe a weird performance problem while trying to rsync .vhd image
files from xenserver to linux backupserver.

i have broken the problem down to a single 500gb file which gets
pathological slow on subsequent runs.

rsync begins with decent speed (250MB/s), i can see that with --progress
and also verify with iotop.


After a while, rsync performance drops down to <3MB/s where i see cpu at
100% on the sender side.


I'm using rsync in daemon mode, receiver is 3.1.2 and sender is 3.1.1.
No encryption or compression in place.


What is causing this slowness?

I know about
https://www.anchor.com.au/blog/2013/08/out-tridging-tridge/, but
according to that article, the problem should have been adressed.

Is there still possibility for "pathological slow performance" which
lies in algorithm/design? (as it does not look like a server/system
performance for me)

regards
Roland