If you’re going for redundancy for uptime reasons, I’d say you’re off to a bad start by putting them both in the same data center, let alone the same host. I’d go for two different data centers, preferably in two different states, with failover DNS.
If you just want it for backup reasons, beyond your own backups and the backups DH keeps, then you could just go with an off-site backup service. I’d probably go with Gnax for that.
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