My energy efficient NAS & general purpose server

[bastiaan]

Hi,

I thought I'd do a little write up of my two-year project for getting an energy-efficient NAS and general purpose server running. I say two years, but during that time I only worked on it during the rare moments when I was really bored.

Anyway: let me elaborate on what I wanted. The main purpose of of the NAS would be data storage (duh), but I also wanted a fully functional system that could run things like revision control services, a nightly email backup, or whatever. So I needed a general purpose operating system.

Given that I wanted power usage as low as possible the embedded systems (i.e., ARM) market was the obvious place to look. Nobody seems to sell general purpose operating systems on NAS hardware, so I started looking at devices that could be rooted and flashed. I eventually decided on the Seagate GoFlex Net:

(Drives not included.) This puppy has a LAN port, a USB port and two powered internal SATA ports, which played into my hands because if I had had to go with external drives that would have meant more wall-warts, and that's bad for power efficiency and it increases my irritability. The GoFlex Net retailed for something like $50 at the time.

Seagate left the door open for reflashing by offering root access, which is a major selling point (I offer this as advice for any manufacturers listening in). There is an active community for the GoFlex (and similar ARM devices) that provide step-by-step guides for reflashing the device and installing debian or Arch Linux. The process is easy enough, and along the way I learned plenty about the uBoot bootloader after making mistakes. The GoFlex can boot from either a SATA or USB drive after reflashing.

The GoFlex's SATA ports allow you to connect any SATA drive, but only Seagate's special GoFlex drives fit snugly and securely. To get around this I bought internal SATA+power extension cables for $1 on Ebay, which allow my drives to be mounted elsewhere.

Then I hit a major obstacle. The GoFlex wouldn't power my 3.5" drive! While researching the GoFlex I missed the fact that it can only power 2.5" devices: +5V only. As it turns out, even though the power supply provides +12V, Seagate hadn't hooked up the +12V line to the SATA power connectors. Possibly they had doubts about the power supply, or perhaps because their 'GoFlex' business strategy didn't involve 3.5" drives.

I was very excited to read about a hack to get the +12V line connected to the SATA power connector:

The downside here was that it requires taking the device apart and to do some soldering, which I hadn't done in at least a decade. I eventually decided to try it and bought myself a soldering iron. The soldering itself was fairly easy, but the GoFlex board fit so snugly in the casing that it was difficult to get it back in. With persistence and patience I won the battle in the end, but only to discover the GoFlex had stopped working altogether. After a lot of dis- and reassembling I finally realised that my new +12V solder points were making contact with the heatshield. The solder points were quickly masked and everything was ready to go. And I'm not ashamed to tell you that I was more than a little surprised to find that the 3.5" drive I hooked up actually spun up and worked as expected!

During disassembly I had unhooked the front capacity indicator LEDs, and decided to keep them that way because I have no use for the indicators. This dropped power usage by 1W! So here are my power measurements at the wall, with note of the devices connected:

• USB stick: 4W
• USB stick + WD10EADS, idle: 7W
• USB stick + WD10EADS, read+write (data sent over network): 9W

I'm very pleased with the results. I plan to eventually replace the hard drive with a 2.5" drive, when high capacity models become affordable, in order to shave another 3-4 Watts from the power consumption, even though it will render my soldering unnecessary. And of course it would be nice to have a small NAS enclosure instead of the midi tower that currently houses my NAS.

[johannes]

Thanks for the interesting write-up! I had been looking for an inexpensive ARM board with two SATA and at least one Ethernet connector to build a small and highly energy efficient NAS using 2.5" drives. This looks like it could fit the bill.

[bastiaan]

I think it might: so far as I'm aware this is the only small ARM board that has more than one powered SATA port.

Having said that, you might also consider recent Intel SoC boards, such as boards based on the Celeron J1800 now hitting the market, which promise very low power consumption while providing much more flexibility than an embedded ARM board.

[bastiaan]

Thanks for the interesting write-up! I had been looking for an inexpensive ARM board with two SATA and at least one Ethernet connector to build a small and highly energy efficient NAS using 2.5" drives. This looks like it could fit the bill.

I was thinking that it should be possible to build an even more efficient system using a Raspberry Pi, a powered USB hub and a few USB-powered SATA->USB converters.

The Pi is very efficient and can run on as little as 2W, which could mean a total power envelope of 3W idle and 4W at load, if the USB hub's power supply is also efficient. The Pi also comes with substantially more RAM than the Seagate GoFlex Net. Although, if you are content with model A's 256MB, you also get about half the power consumption.

A possible downside is that you won't have SATA transfer speeds at your disposal. However, your throughput is already limited by the ethernet connector to speeds lower than the USB2.0 maximum transfer rate, even with the GoFlex. So unless you do a lot of transfers between two simultaneously connected hard drives, this won't be an issue for you.

The other caveat is that you must be sure that your 2.5" drives will run on USB power alone. The manufacturer's specs should be able to tell you this.

[HellDiverUK]

The Pi is a terrible NAS unit. The NIC runs off the already quite broken USB bus. Asking it to run two drives as well is a disaster waiting to happen. You'd be better off with a cheap TPLink router and running OpenWRT or something similar on it, at least the USB works properly on those, and you have a proper gigabit interface.

[bastiaan]

The Pi is a terrible NAS unit. The NIC runs off the already quite broken USB bus. Asking it to run two drives as well is a disaster waiting to happen.

Yes, I was thinking the powered USB hub would power the drives, and possibly the Pi itself as well.

You'd be better off with a cheap TPLink router and running OpenWRT or something similar on it, at least the USB works properly on those, and you have a proper gigabit interface.

But presumably a gigabit interface would be most useful if those USB ports were USB3, right?

At any rate, I like this idea. Do you know of any particular device that would meet these requirements?

[washu]

Yes, I was thinking the powered USB hub would power the drives, and possibly the Pi itself as well.

The issue is not one of power, but of speed and reliability. The USB bus on the Pi is highly broken and cannot even come close to normal USB2 speeds.

But presumably a gigabit interface would be most useful if those USB ports were USB3, right?

USB2 is not the limiting factor, the Pi's broken USB bus is. It cannot even do full speed 100 mbit networking. USB2 will not max out gigiabit, but it can go higher than 100 mbit and much higher than a Pi.

[bastiaan]

Very interesting, thanks!