Hi!
As I’ve no previous experience with SAN storage in my environments I apologize if my answers are not accurate. I’m sure you’ll get it running.
About your copy error, as you mentioned that you’re using CentOS 7, is SELinux enabled? If not I guess you’ve checked that you can write flawlessly in the /var/lib/one/datastores/101 folder… sorry those are my usual troubleshooting steps 
And I’d like to correct myself on my first answer, as Carlos answered here (Ssh system datastore capacity) when using SSH datastores: “the capacity is supposed to be inside each one of the host information (host tab, or onehost show). This is because each host will have a different local storage.” So you were right using onehost to show datastores capacity.
Cheers!