Whimfield

Low-power server

Posted on 02. Aug, 2008 by Cameron in Projects

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This post was written by Cameron!

One of the main goals we have with our house is to make it as cheap as possible to live in. With the cost of electricity being the most expensive in all of Canada here on PEI ($0.19 kw/h + $30 per month flat fee), we are looking for ways to cut back on our electricity usage. Our ultimate goal is to consume 0 watts when the house is idle–that is, when we aren’t using anything, we shouldn’t be paying for electricity.

After tackling obvious things like, how do we heat our hot water, we went on to other, less weighty, but still sizeable consumers. One of these consumers was our old, noisy, dirty, and dated headless server, Kibo. Kibo has been in our family for many years, acting as our network server. Kibo allowed us to share our files, centralize our email, download torrents while our laptops are preoccupied, etc. Kibo was great.

But the unfortunate thing with Kibo is that it sucked up a lot of power with its two IDE drives, dual P3 processors, and decade-old technology. Kibo cost us roughly $170/year in electricity. Too rich for our blood.

After toying with the idea of replacing Kibo with a cheap router and losing functionality, I decided that there had to be a better way. The solution I came up with for this problem was to look for a router that could run OpenWRT and supported external storage. The router of choice was the Asus WL-500g Premium with its two USB ports. Combining this router with a 2.5″ laptop HD in a USB enclosure seemed like a good solution, so we bought the USB-powered 160gb Seagate Freeagent GO.

Like most USB-powered external HDs, the Seagate Freeagent GO came with a Y-cable with two USB heads. The reason there are two heads on the cable is that the USB specification only allows for 500ma of current to be supplied from any one USB port. This is where it gets tricky. Sometimes this limit is not enforced, but sometimes it is. Seagate claims that their HD may need upwards of 1A to spin up, so, even though one head may be sufficient on one computer, two heads may need to be plugged in on another.

However, when I researched this subject I wasn’t at all concerned about the USB power issue as the WL-500g Premium convienently came with two USB ports anyway.

Once the router and HD arrived I spent a few hours setting up and installing OpenWRT. I was sure to plug both HD heads into the back of the WL-5oog Premium, to ensure it had sufficient power.

Well, it didn’t work! Nope, the HD just sat there clicking away–it didn’t have enough frickin power to spin up. What’s the point of having standards if manufacturers can’t even follow the specs, I thought to myself. After looking around online for a bit, trying to find a solution to my problem, I realized that this setup was a little too obscure and I wasn’t going to be handed a solution on silver. So, I came up with my own solution.

I had a hunch that the Seagate HD was consuming a little more than 1A on spin up, and with the Asus WL-500g Premium being a low-power device, I was guessing that it was going to be pretty strict about the 500ma restriction. So, the first step was to reduce the power consumption of the Seagate HD.

I disassembled the HD’s case and ripped out the huge crazy-glowing-alien-like LED. I mean, come on Seagate, what a waste of power.

After ripping out this atrocity, I attempted to try the HD again. No dice, but it was definitely a lot closer to spinning up.

My next step was to try and give the HD more power. Use a self-powered USB hub you say? Yes, that would work, but then one needs to use another wallwart, another lossy AC/DC transformer, inefficient I said! I found a better way–subvert the USB spec altogether. The WL-500g Premium just so happened to be powered by 5V, the same voltage USB uses.

I took the router’s adapter and spliced in a female USB connection connecting the red wire to the adapter’s +5V wire and the black wire to the adapter’s GND wire.

With this setup I was able to plug the Seagate HD’s first head into the Asus WL-500g Premium as I had it before, but I was also now able to plug the second head directly into the female USB connection, giving the HD all of the additional power that the adapter was able to supply.

It worked! The HD spun up and I was able to access the drive. After I disabled the Seagate FreeAgent GO’s lovely internal 5 minute auto-spindown “feature” to prevent OpenWRT from barfing out pages of IO errors, I was off to the races.

The little router has 160gb of shared storage, it acts as a firewall, a switch, a wireless router, and it is more than happy to run all night downloading our torrents while our laptops are turned off. Sweet!

If you were able to read the specs on the WL-500g Premium’s power adapter above, you would have noticed that it’s only capable of supplying a maximum of12.5 watts. You may have also noticed that it is a switching adapter with CEC efficiency level IV. What does that mean you ask? Well, it means that the setup is very efficient. I have yet to measure the actual consumption of the setup, but I estimate that it consumes roughly 6-10 watts on average during normal usage. This translates into a yearly consumption of approximately 70 kw/h–an electricity cost on PEI of only $14 a year and over $150 a year in savings over our beastly Kibo. And, best of all, the savings came without sacrificing any functionality.

So tonight we will say goodnight to our old friend for the last time. Good night Kibo.

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