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Low-powerered Ethernet Hard Drive?
WotPeed asks: "The company I work for builds extremely sensitive electric and magnetic field sensors. The project I'm just starting needs to use a hard drive to store the digitized data for long-term measurements (no more than 20GB). Unfortunately the hard drive has to be external to the sensor because it generates too much magnetic interference (hard drive needs to be at least 20 feet away). I'm therefore building an ethernet link into the sensor so that it can connect to a remote hard drive. Wireless is an option for a later revision but we're going with wired ethernet at first to keep things simple. There are plenty of network attached storage devices out there but they all assume they will be used in an office environment, and therefore consume a LOT of power. I'm looking for an ethernet hard drive that consumes less than 10W (this system will be used outdoors and runs on 12V batteries). Does Slashdot have any suggestions before I roll my own? I don't need any of the fancy features found in most NAS solutions...I just want a hard drive I can FTP to."
I'd think you'd have to roll your own. That said, it shouldn't be too hard to do. Just take a laptop drive, interface it to a microcontroller (search Google and you can find code and such to interface PICs, Amtels, HC11s, and others to HDs). Add ethernet (either a ethernet chip, you can find info on interfacing those with the same microcontrollers) or just use a reliable ISA card (3c509s are very well documented) and connect that to the microcontroller (also easy to do).
Comment forecast: Bits of genius surrounded by a sea of mediocrity.
The slowest Seagate 20GB drive i found consumes 24 watts. You'll still need an interface - cpu, memory, network... /." help. If it's a power availability problem - spacecraft maybe?... you're not looking for a COTS solution... there would be none. If it's a power DENSITY problem... consolidate all the drive needs in a server away from the environment you're measuring.
You're talking about NAS. So far, as you note, that's always been an office thing. They're made with ready power and heat dissipation taken for granted. I can't imagine a company with a real need for such a specialized requirement (as in, you're about the only case it's ever been needed) needing "ask
Incidentally, just so you don't embarrass yourself in front of your boss... wireless, at least in the most-commonly used sense, uses both electric and magnetic fields, most commonly at 2.4 or 5 GHz. Hell, conventional ethernet is something like DC-UHF, but mostly contained in the cable... perhaps something optical might be better-suited to your needs?
Frankly, I think I'd take the DC outputs of the sensors and route them as the center conductors of good-quality coax, and bring them all to a bank of A/D converters somewhere away from the environment being measured.... can you give some kind of detail about the environment?
Anyway, when you roll your own, you'll have to use something like a Hitachi microdrive. The 1GB drive consumes 8-1/4 watts on write. Maybe a transmeta-based motherboard won't break the rest of the budget.
I'd be glad to work on it. I need a job.
Assuming it is average and you are doing long term measurements, the average data rate must be pretty low (relative to hard disk transfer rates). So, I would add RAM to the sensor end controller and cache information there until you hit lets say 80% cache full, then fire up the hard disk and do the writes.
I would use USB 1.1 for the link, controllers are easy to find and cheap, the power requirements are much lower then ethernet+microcontroller+drive interface.
If your power requirements are peak, then put a lion battery on the hard disk end, charge it from the USB power and operate the drive from that.
If cost it not a huge issue, you might consider 10 2GB compactflash cards. That would eliminate the need to implement the remote data link.
Sure, but once you specify FTP you then need TCP, which means you need IP, and an FTP server, and a filesystem, and Ethernet, and ... you've just specified a NAS.
But the problem didn't require a NAS. Your problem was "too much interference so need the hard drive 20 feet away". You could solve this problem with Fibre Channel.
Investigate an external disk enclosure with fibre channel and a DC power supply. I know Sun was selling these just 2 months ago for desktop external disks.
There are plenty of bus-powered USB drives for use with laptops. That's the lowest-powered external drive you are likely going to find.
Don't bother with Ethernet-attached storage; those are not usually designed with low power in mind.
The personal server is not an actual product. Just an interesting concept.
You bit bang it with a mircocontroller.
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