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Author Topic: Safe to turn on/off external scsi drive?  (Read 1543 times)

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Offline Floid

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Re: Safe to turn on/off external scsi drive?
« on: March 08, 2005, 02:58:26 AM »
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MrZammler wrote:
@ChaosLord

LOL, ok, seems safe to me then! thanks!


SCSI is supposed to be resilient like this.  :-)  However, if you have multiple devices on the chain, you want to watch out for termination issues if nothing else -- if, say, your internal HD is on the same chain, and the external device is both providing termination on the external end and providing TERMPWR for the bus, you can expect to risk flakiness on the chain when it's switched off.

Note that TERMPWR is supposed to be provided by the 'initiator' (read 'the controller'), so you should be safe, as long as you haven't gone around jumpering your external stuff to ignore it and take it from the drive PSU (or it didn't come like that to begin with).  

Meanwhile, for that concern raised in the above -- how long is 'longer?' -- it can be a good idea to jumper that way, let your external box power itself (the "TERMPWR to on drive terminator only" option some peripherals present), and practice power hygeine (read: not turning the terminating unit's PSU off if you have other peripherals you need to keep using on the same chain).  You only reallly have to worry about this if you're having termination-related bus problems, or are paranoid about avoiding them.

(Call me stupid, but active terminators *do* still draw or have-the-option-to-draw from TERMPWR, right?  How else could they make them standalone?)