UPDATE: To simplify resetting it to the default, without having to calculate 50% of your RAM, you can set the value to “0” in your Startup Init command, and then reboot.
echo 0 > /sys/module/zfs/parameters/zfs_arc_max
You might have better luck with a “Pre Init” command.
If that doesn’t work, then go ahead and manually set the value in your Startup Init command. See @cmplieger’s post above.(You might not be able to “set” it to “0”, since SCALE likely sets it to a different value shortly after bootup. And it doesn’t accept setting it to “0” on a “running system”.)
Nevermind. Only use @cmplieger’s method to return to Cobia’s bevhaior. See this post as to why.