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List:       linux-raid
Subject:    Re: Hot-swap?
From:       Chad Robinson <chadr () brt ! com>
Date:       1997-09-24 14:26:34
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On Mon, 22 Sep 1997, Ingo Molnar wrote:

> > What are the problems associated with pulling an IDE drive off `live', and
> > then replacing it with another drive?  Without true hot-swap SCSI RAID, I've
> > always been a `with the system down' kind of guy, but what EXACTLY can you
> > do hot?
> 
> this is clearly out of spec for normal IDE systems. I've plugged off disks
> already to simulate hard failures, but never tried putting them back ... 
> 
> Probably, for RAID-1 systems it will work, if you do a 'flushb
> /dev/md0;flushb /dev/hdc' before putting a new disk onto the bus, and you
> should use identical disks. But i've _never_ done this, if anyone else has
> experience, please speak up .. ;)
> 
> the IDE and RAID code handles it properly, ie. we get errors on a few IO
> requests, then mark the disk failed and never use it again. So you are
> free to remove the disk and add it back to the array, which starts a
> resyncing.

Oh it's quite out of spec, I know, but my primary interest is in knowing
whether or not it will damage the bus electrically.  I'm not familiar with
the signals visible on the IDE bus, but the controller isn't the only one
sending signals down.  From my understanding the drives communicate with
each other, although new EIDE standards may have changed that (at least, my
BIOS is perfectly happy with a slave CD-ROM drive and no master on that bus).

So what, electrically, would happen if I plugged a (presume it's already
powered up, or maybe that's worse?) new drive into a running system?

Hypothetically, of course.  Hardware SCSI RAID is always available and
they're not all that expensive these days.  It's an interesting idea, though.

-----------------------+--[ Chad Robinson (Task) ]-+--------------------------
Senior Systems Analyst |                           |             chadr@brt.com
BRT Technologies, Inc. |                           | http://www.brt.com/~chadr

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