Gluster probably is not the right solution to your problem, because:
with only two servers, it is going to have low random IO performance;
your total write bandwidth will be limited by the server with HDD pool.
I would suggest using ZFS with async send/recv from the SSD server versus the HDD one, but consider that you will need to coordinate a manual ...
Deciding if/when to make a failover or server redundancy is a matter dependent on several factors: resources, type of target service, type of backup you have, your uptime/downtime/recovery time target.
The most simple scenario of all is if you have a backup that supports instant recovery.
This can cover most general use situations. You're up in 2 minutes and ...
Running 2 guests inside the same host defeats the purpose of redundancy.
Make a guest server on a separate host on a separate physical server.
Configure the print servers as primary and secondary.
Since you already have the primary, follow the guide here to make the secondary one.