Mr.Jason wrote:

> My last post close to this topic gave me more information I could imagine
> in
> my wildest dreams. (About humans & electric conducting as well!)Thank you
> everyone.
>
> I'm curious. Lets say you have two HD's on your linux box. The secondary
> you
> use much as a backup medium. Then you want to replace the secondary drive
> while computer is on.
> If you spin down a hard disk is it OK to remove it and replace while power
> is on? I suppose not, but please speculate and analyze the events of
> hotswap ordinary IDE disk. Would it make difference if the disk is on
> mobilerack or not?
> Professional electricians are welcome to join this conversation and give
> your opinions!
>

You asked for it :^)

The typical failure mode for hot-plugging digital devices
is latch-up. The CMOS technology used to drive the pins on
a chip creates a structure similar to a thyristor (SCR).

If current above a certain (very small) limit is injected
into a pin *before* power is applied to the chip, latch-up
occurs. Both drive transistors switch on, shorting the
chip's power rails.

When supply power is applied, the transistors blow, letting
out the magic smoke.

Devices which are specifically designed for hot-plug, either
use chips which avoid latch-up by design or make sure that
power is connected before any other signals. Have a look at
an USB or CompactFlash connector. The power pins are mechanically
different and connect first.

Specifically, IDE hard drives have separate power supply
connectors. If you want to risk it, it's probably best to
hot plug the data cable while the disk is powered up.

Some trays allow hot plugging, others don't.

Get an USB2 enclosure for your disk. Much safer.

Kind regards,

Iwo