Not too long ago, Amazon released their Simple Storage Service (or "S3" for short). It provides a hosted storage platform which developers can build all sorts of applications on top of. Smugmug, a popular photo sharing web site, is using it to store and host pictures.

I've been considering using S3 as the backend to an on-line backup, since I'd been beating that for a while (see: Swimming Pools and Hard Disks and Cheap On-Line Storage Coming Soon).

In a few days I'll write about how to do this--I'm only partially through the process right now. But right now I want to lay out the motivation for doing this.

The Cost of A Home Server

Amazon's pricing model is pretty compelling. The current rate is that I'd pay $0.15/GB monthly for the data I store. Data transfer costs $0.20/GB.

My home server is a 2.4GHz Pentium 4 that contains 3 250GB SATA disks in a RAID configuration, plus an 80GB boot and OS disk. I decided to measure its power use using my Kill A Watt and found that it consumes roughly 120 watts of power with the CPU idle and disks spinning. That's about 80 kilowatt hours every four weeks. According to PG&E's Residential Rates, the average cost of electric power in San Jose is $0.16247 per kilowatt hour.

My home server costs me a minimum of $13 every four weeks just to leave powered on and idling, or $170 per year. That doesn't count the roughly $700 I sunk into the disks and the other $700 I likely spent on the motherboard, CPU, case, RAM, and so on. Remember, these are absolute minimums, since the CPU does consume more power when it's actually doing work.

So if we assume that I spent $1,400 on the server and would keep it for 5 years, that's another $22 per month (4 weeks) of costs.

If you're keeping score, that's $22 + $13 = $35 every four weeks just to have backups of my stuff (most of which lives on servers in a few datacenters).

That puts the total cost for 5 years worth of backups around $2,275 assuming that no hardware breaks.

The Cost on S3

My backups require about 125GB of disk space today without compression. That'd cost me $18.75 per month to store on Amazon's S3. Let's further assume that I increase that by 1GB/month for the next five years (mostly photos) and transfer about 2GB every week doing backups (log files, mail, and other temporary stuff is much of that).

2GB every week is 8GB every four weeks, which costs another $1.60 every four week "month" for a total of $20.80 per year or $104 over 5 years.

Assuming that growth rate has me up to 190GB five years from now. Let's call it 200GB. If I'm growing at a constant rate, I can use the average of 200GB and 125GB, which is 162.5GB. Multiply that by 13 "weeks" and 5 years yields $1,584.

Adding it all up, if those guesses are right and we assume that Amazon's prices don't fall (they certainly could in a few years), I'd end up paying $1,688.

In other words, switching to S3 could save me $587 over five years!

Other Benefits

It's clear that going with S3 could save me money both from a reduced electric bill and not having to buy backup hardware (server and disks). But why else might I do this?

Availability. It's less likely that Amazon's service will go down when compared to my home server and residential grade broadband service.

Speed. If a remote server dies, I'd need to push all the bits there from my artificially slow DSL or Cable connection at home. Using S3 means I can restore faster.

Simplicity. This is one less Unix box I have to spend any time administering. Even if it's only 5 minutes every week or two, that all adds up.

Again, I'll write up the process (tools and stuff) in a few days (or weeks).

Update: The economics are even better than I thought. It turns out that I mis-read some du output last night. I really only need half the space I thought I did. That is, ~75GB today instead of 125GB. Hmm...

Posted by jzawodn at October 03, 2006 08:51 PM