When should I recommend Cloud solutions to my clients? I don't know. Today I'm going to start figuring it out. I'm going to compare an on-premise build with a cloud based solution for a hypothetical 50 employee organization. Allow me to skip a lot of details and say it will provide roughly equivalent features and security. Anything required in both solutions was a wash and therefore ignored. What you're left with is mostly a lot hardware (servers, SANs, firewalls, switches for iSCSI, etc), deployment services and hardware-level support.
NOTE: All pricing is retail and rounded. Individual proposals may vary. A greenfield is assumed - no data migration. Everything that was common to both solutions was excluded so this may represent a small portion of the overall project.
Cloud Offering:
In the cloud we'll procure 20Ghz of processor capacity, 50GB RAM, 3 TBs storage with 10 Mbps of bandwidth to host 15-18 Virtual Machines. Onsite backup for 1.5 TBs. This will run about $10,000 per month.
On-Premise Offering:
On-premise will provide provide about 60Ghz (over 24 cores), 96GB RAM, 3TB direct attached storage for backup, 3TB iSCSI SAN. We'll plan on hosting 25-30 VMs on this platform. You'll get this for about $160,000 including 200 hours for installation and configuration. See my build here. Note we dropped 25% of capacity for high-availability.
To even the playing field we have to factor in datacenter costs for the On-Premise Offering. I see a rack, 10Mbps of bandwidth, and 40A of power. Say $3000 per month?
Conclusion:
Let's compare 3 years of costs. In the cloud you're out $360,000. At home, including the data center costs, you're looking at $268,000. The $92,000 delta has to cover the hardware support and maintenance for 3 years. There is some difference in capacity and reliability. I hope it helps your evaluation to say that the cloud offering, in this case, is 35% more expensive.
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