SCSI tape drive removal, hot remove, termination?

Firstly, thanks a lot for your help

I may have put you wrong here its external and has a terminator plugged in to the drive at the yellow arrow. (See jpg)?
ExternalDrive.JPG

Power off the drive and unplug it is no big deal.

No different that unplugging a parallel printer from a PC.

You will have to have it plugged in and turned on when you reattach it to a powered off file server,otherwise the SCSI card won't detect it.

But there shouldn't be an issue.

I agree with Labsy.  DON'T JUST UNPLUG!!!

I was just too slow to type :^(

Robstg

I've been dealing with SCSI for over 30 years and it won't hurt it.

SCSI is a communications protocol not unlike parallel or serial.

Believe it or not,parallel printers are terminated.

Would you power off a filer server to remove a parallel printer or serial mouse?

Of course not.

So, what you are saying pgm554 is that you know for a fact that rexwithers only has that tape drive in the chain?  And that no other device would be affected?  I don't recall rexwithers mentioning that it was the only device connected... But, if you already know that, kodos.

Amazing how 30 years gives you great insight like that!

I remain humbled,

Robstg

Did you see his diagram?

External drive with active terminator.

Nothing else on the SCSI buss.

As I said ,no big deal.

Look its OK to down the server is that's even possibly safer, thanks very much for all the suggestions.

Rex, from diag you posted, it looks like you have a HP StorageWorks Ultrium 920.  

If you need difinitive answers, here is a link:

http://bizsupport1.austin.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c00850581

@pgm554 if you are trying to make me believe that (again) you know what is at the other end of the cable, kudos.  I went with the assumption that this MAY be the last hat box in a daisy chain.  

Cheers,

Robstg

If he had multiple boxes daisy chained,my best guess is he might have mentioned it.

And even then,just attaching  the terminator to the next device in the chain would have fixed any issues without having to power down.

Done it many times.

So telling him to power down was a bad call?  Seems that your assumption that "he might have mentioned it" goes against good troubleshooting skills - especially that he says "I haven't had any experience with SCSI before".  

Why would you think he would know to tell you that he has a daisy chain?  Your "no big deal" answer is what irked me. If he came to us "experts" to guide him through this issue, and you tell him to "just unplug" and he kills other devices - how is he to know that by moving the termination point would solve his issue?  Anyway, you do know what you are doing...  I just felt you took way too much for granted in your answer.

Cheers,

Robstg

I've written SCSI protocol code since the 80s (yes this dates me).   If you power it down, or unplug it, then you will get a bus reset.  The bus reset will typically cause any I/Os on the chain to abort.

If you DO NOT have anything else on the chain then unplug or power off.  It doesn't matter.  

If you DO have something else on the chain, then unplug it or power off.  It doesn't matter.

Either way, you will get a bus reset.  If your initiator, device drivers, and applications will automatically retry after a bus reset then no harm no foul.  If they don't, then you are screwed either way.

Pretty much sums it up.

You do not need to power off a file server to remove an external SCSI device.

Is there a chance it could hang your server?

Yes, about the same as unplugging a USB device,printer ,mouse or keyboard.

Well, pgm554, I will say that I have seen a both yanking and cutting power on a device in the chain abort a program that was doing I/O to other devices on the chain. In fact, I fixed a bug relating to this very issue earlier this year.   The bug was really more of a feature of the code , and had nothing to do with the hardware or drivers.

So you can cause a crash or even a hang (but hanging is rare), so I can see how somebody sees a bad thing happen after yanking a hot device and they automatically think that yanking the device is a bad thing and dangerous in as of itself.

It isn't.  Either one is running well-written code or they aren't.  The problem is that only the developer knows for sure, so the safe thing is to be conservative and schedule down time.  

But that is always the smart thing to do, along with always backing up before making hardware changes.

Thanks everyone, bit of a hard points decision. In the end I guess the more conservative and "best practices" type solution needs to be one one I use. Job done thanks.