Computing stuff tied to the physical world

Hard disk power control

In Hardware on May 30, 2011 at 00:01

There’s a server running 24 hours a day, 7 days a week here at JeeLabs. It has two internal hard drives, one of them used as hourly backup for the system partition on the other disk. It’s running a couple of VM’s with all sorts of services, and it’s been running flawlessly for several months. Draws 10..15W.

Now, I’d like to attach a couple of extra hard disks to this server. A pair of disks for off-site backups (yes, there is a daily cloud backup, but I want a second fall-back system for some files), and a disk with stuff I rarely need, but don’t want to throw away. Disks are cheap – in fact I’ve got enough disks, so disk storage is actually free here. And while I’m at it: maybe add a little NAS for private stuff, since it’s been lying around and collecting dust anyway.

But I don’t want to have everything on-line all the time, for safety reasons and to keep power consumption low.

Why not use a JeeNode to control the power to these devices, which all run off a 12V supply? And why not just use one beefy switching supply, instead of that endless collection of power bricks?

Here’s a first idea:

Screen Shot 2011 05 29 at 18.49.52

Only one of the two channels on the MOSFET Plug is used here. And instead of switching a power LED or LED strip with it, it’s being used to control the power to the external disk drive.

There’s a flaw in this design, though: it’ll only work with ONE hard disk…

Tomorrow I’ll go into this and explain what’s going on, and why it can’t work with multiple disk drives. Hint: this setup only works if the JeeNode is controlled by wireless.

  1. Are you sure about this JC? I thought hard drives (at least regular 3.5″ drives) need 12v for the motors and 5v for the logic circuits?

    Plus, you have to make sure the drive is unmounted from the OS or you risk losing data from the cache, and the OS not recognising the drive when you power it up next. This is certainly what’s happened to me in the past when I’ve tripped over the power lead of a USB hard drive connected to windows!

    My last concern is one of reliability. The start up process is the most stressful time for most devices, from light bulbs (plink) to cars and electric motors. The current demand for a stationary motor is much higher than a running motor. I’ve seen many more hard drives discovered as dead when they are powered up than have actually died whilst running.

    • Hang in there… I’ll address (at least some of) your concerns in the next posts.

  2. :-D

    I doubt it will surprise you to find out that I hate TV programmes that have “to be continued…” on the end so much that I check before watching them, and if it is of the offending type, record it and don’t watch it until I have the concluding episode!

  3. Well, TankSlappa- my thinking is currently centered on the fact that he’s switching the ground lead. In most systems, unless you’re using optical fiber, the grounds must all be connected together for signals as well as power…

  4. Or he will do the backup to his car, which has 12v and only a wifi connection to his network. The on/off mechanism is needed to prevent his car battery getting empty. ;-)

    • Speaking of which – last Friday, our car had to be towed to the garage because… the battery was empty! (it died, after 10 years of service)

    • I’ve already got a car like that… Got a lovely 60watt DC-DC power conditioner, provides 12v even when cranking the engine and the supply drops to about 9volts. Also sends an “off” signal to the PC board, and keeps the power on for 60 seconds before shutting off completely.

      Really should give it an upgrade sometime, it’s only got an 80gig drive :-)

  5. Hard disks can also be powered down from software. Admittedly the power consumption won’t be zero, but when the platters stop spinning it probably isn’t much more than a JeeNode.

    If you’re using Linux look at the hdparm command, especially with options -C, -y and -Y for testing and -S to have a disk automatically spin down after some time of inactivity and be automatically powered back on by the kernel when needed.

  6. How about using the hard drive’s own methods for powering down when they are not needed, either with their builtin idle timers or with explicit power down commands from the host?

  7. I hear ya – the built-in spin-down command is the obvious way to do this, and indeed what I’m doing now.

    But… I really want total power off, an off-line mode which isn’t controlled by the attached computer (accidental spin-up & long-term archives), a way to control other 12V devices (NAS & label printer), an maybe also a second unit for 5V-powered devices.

    Lots of refinements possible: automatic staggered power-up, turning a master computer on triggers a set of slave devices on another computer, trigger on activity in the house, secure access via internet, etc.

    The way I see this is as a DC plug extender/distributor with built-in remote-controlled switches.

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