While using rsync on ESXi 7 to copy files and directories from one ESXi datastore to another remote ESXi datastore, the screen fills with “rekeyed outbound cipher rekeyed inbound cipher” messages about every 10 seconds. There is a way to fix this.

There is a setting in /etc/ssh/sshd_config that I commented out and changed to RekeyLimit default none.

# vPP FCS_SSH_EXT.1.7: rekey after 1GB, 1H (instead of default 4GB for AES)
RekeyLimit default none
#RekeyLimit 1G, 1H

Restart the service on the target ESXi.

/etc/init.d/SSH restart

Stop the rsync from the source ESXi and restart it. No more messages.

What is the rekeylimit?

     RekeyLimit
	     Specifies the maximum amount of data that may be transmitted or
	     received before the session key is	renegotiated, optionally fol-
	     lowed by a	maximum	amount of time that may	pass before the	ses-
	     sion key is renegotiated.	The first argument is specified	in
	     bytes and may have	a suffix of `K', `M', or `G' to	indicate Kilo-
	     bytes, Megabytes, or Gigabytes, respectively.  The	default	is be-
	     tween `1G'	and `4G', depending on the cipher.  The	optional sec-
	     ond value is specified in seconds and may use any of the units
	     documented	in the TIME FORMATS section.  The default value	for
	     RekeyLimit	is default none, which means that rekeying is per-
	     formed after the cipher's default amount of data has been sent or
	     received and no time based	rekeying is done.

https://man.freebsd.org/cgi/man.cgi?sshd_config(5)