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I've got two hard drives running two different OS. I need both of them, but want to run them on separate drives without dealing with the struggle of switching the cables every time.
I suppose cutting the power of the HDD that's not in use should do the job(?). But when I stumbled upon this switch it specifically says:

[...] NOT to be used to for hard drives, optical drives, etc.

Disregarding potential problems with the BIOS that may occur, is there a physical issue that I'm missing here? Why should you not use that kind of switch for a hard drive?

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migrated from electronics.stackexchange.com Jun 5 '13 at 23:02

This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.

    
The hard drive may be bus connected and removing its power does not disconnect it from any bus thus it will leave circuits connected to the bus with no power and possibly slow the bus down or prevent it working correctly. –  Andy aka Jun 5 '13 at 20:15
    
Is there a reason normal dual booting won't work? –  Karl Bielefeldt Jun 5 '13 at 20:19
    
Of course, dual booting would (and will have to) work as well. It's just that I would've prefered this "cleaner" way of having one OS per drive. –  hcrudolph Jun 5 '13 at 20:40
    
It's not recommended to immediately accept an answer, to stimulate discussion and potentially attract more answers to the question. (24 hours is the "accepted minimum".) Upvotes should be used liberally. –  Adam Lawrence Jun 5 '13 at 20:40
    
Thanks for the advice. I'll hold on to it! –  hcrudolph Jun 5 '13 at 20:50

3 Answers 3

up vote 1 down vote accepted

You don't want to remove power supply from a hard disk while other signals are still attached. You always have to make sure that power supply is connected first before other signals are attached. Same goes for the reverse. First disconnect the signals then the power supply. A hard disk by itself is not hot swappable. You may blow some parts of the internal circuitry otherwise.

It has to do with the fact how a semiconductor is built. Almost any IC can latch like an SCR when voltages are applied before power supply is available. This means (uncontrolled) high currents at places (on the die) that are not designed for them.

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You can find further evidence supporting this recommendation by examining an USB cable. The contacts for pins 1 and 4 (+5VDC and GND) are longer so the power pins are the first pins to be connected and the last to be disconnected, even though there may only be a split-second difference. –  rob Jun 5 '13 at 23:49

You're doing it wrong. I have two independent OS installs, with separate bootloaders. Simply install one, then the other, then quite simply use the bios to switch.

Alternately look at hot swappable bays, and simply pull out the caddy when you don't want that OS.

I note that sata connectors have a limited lifespan (I remember something absurdly low like 50 plug unplug cycles, but I could be wrong), and you don't want to keep plugging and unplugging it.

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A cleaner way is to unmount the drive not needed in the device manager.

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1  
-1: won't help with dual-booting. –  Renan Jun 5 '13 at 22:16

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