# Terminating SCSI bus tape and Zip drive

## VinzC

Hi.

There is a question I have never been able to answer about SCSI termination. I have an Adaptec 2904 SCSI adapter with an internal cable connector and an external connector at the back, an external SCSI zip drive and an internal SCSI tape drive (Archive Python Python 00095-001). The Zip drive has a switch to enable SCSI termination, I think it's active. It is currently enabled. The internal SCSI tape drive has no terminator, I think.

I have plugged the passive terminator (sort of a small, black stub) at the end of the internal cable, while the internal SCSI tape drive is connected to the second connector on the cable. I have also plugged my external SCSI Zip 100 drive (IoMega) with a cable to the connector at the back of the SCSI card.

I've always had troubles with both devices. Meanwhile I've always wondered where I should terminate the SCSI bus:

- Should I plug the internal terminator? and where?

- Should I place the SCSI tape drive at the and of the internal cable instead?

- Should I enable the terminator on the external Zip drive?

- What about terminating when the external Zip drive is powered off?

- Should it be always on? Should I enable only one termination at a time?

Basically: when and where should I terminate a SCSI bus?

EDIT: I don't stop having I/O errors on the tape drive with "mtx" and the orange led always blinks whenever I put a cassette in the drive. In 2 years I have never been able to use that thing  :Sad:  .

Thanks in advance.

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## NeddySeagoon

VinzC,

The SCSI bus must be terminated at both ends of the bus - the physical wire only.

Many devices include terminators, some have a jumper to turn termination on and off. Others require external terminators. Some have terminators and no controls, they must be placed at the ends of the bus. If you have three of those, you have a problem.

A SCSI controller looking after internel and external devices gets a little complicated.

First, are the internel and external devices on the same SCSI bus?

If not, its two SCSI buses and they are treated seperately.

SCSI termination requires power (part of it is pull up to 5v) If the external device provides its own terminator power, it must always be on to terminate the bus properly. (or other devices won't work). There is often an option for the controller card to provide terminator power on the cable, so the end devices do not always have to be powered, however, end devices don't always respect this.

In short, its grown up to be a mess, you need to read all the devices data sheets carefully. Set the end devices on the bus to be terminated, remove the termination from others. Preferablly use cable supplied term(inator) power, so you can switch the end devices, like your Zip drive, off and have everything else still work.

If you have a mix of 8 bit and 16 bit SCSI on the same bus, it gets worse.

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## VinzC

Thanks, NeddySeagoon.

 *NeddySeagoon wrote:*   

> VinzC,
> 
> The SCSI bus must be terminated at both ends of the bus - the physical wire only.
> 
> Many devices include terminators, some have a jumper to turn termination on and off. Others require external terminators. Some have terminators and no controls, they must be placed at the ends of the bus. If you have three of those, you have a problem.

 

Fortunately I think I don't have all three. I think I recall the internal tape drive has (active) terminators. But I didn't enable them. The external Zip drive also has active terminators as I said.

 *NeddySeagoon wrote:*   

> A SCSI controller looking after internel and external devices gets a little complicated.
> 
> First, are the internel and external devices on the same SCSI bus?

 

They all seem to be on the same bus:

```
$ dmesg | grep -i scsi

ahc_pci:0:15:0: Host Adapter Bios disabled.  Using default SCSI device parameters

scsi0 : Adaptec AIC7XXX EISA/VLB/PCI SCSI HBA DRIVER, Rev 6.2.36

        <Adaptec 2902/04/10/15/20C/30C SCSI adapter>

        aic7850: Single Channel A, SCSI Id=7, 3/253 SCBs

  Vendor: ARCHIVE   Model: Python 00095-001  Rev: 5AB

  Type:   Sequential-Access                  ANSI SCSI revision: 02

(scsi0:A:4): 7.812MB/s transfers (7.812MHz, offset 15)

Attached scsi tape st0 at scsi0, channel 0, id 4, lun 0

Attached scsi generic sg0 at scsi0, channel 0, id 4, lun 0,  type 1

  Type:   Direct-Access                      ANSI SCSI revision: 02

Attached scsi removable disk sda at scsi0, channel 0, id 5, lun 0

Attached scsi generic sg1 at scsi0, channel 0, id 5, lun 0,  type 0

```

```
$ dmesg | grep -i scsi0

scsi0 : Adaptec AIC7XXX EISA/VLB/PCI SCSI HBA DRIVER, Rev 6.2.36

(scsi0:A:4): 7.812MB/s transfers (7.812MHz, offset 15)

Attached scsi tape st0 at scsi0, channel 0, id 4, lun 0

Attached scsi generic sg0 at scsi0, channel 0, id 4, lun 0,  type 1

Attached scsi removable disk sda at scsi0, channel 0, id 5, lun 0

Attached scsi generic sg1 at scsi0, channel 0, id 5, lun 0,  type 0
```

 *NeddySeagoon wrote:*   

> SCSI termination requires power (part of it is pull up to 5v) If the external device provides its own terminator power, it must always be on to terminate the bus properly. (or other devices won't work). There is often an option for the controller card to provide terminator power on the cable, so the end devices do not always have to be powered, however, end devices don't always respect this.
> 
> In short, its grown up to be a mess, you need to read all the devices data sheets carefully. Set the end devices on the bus to be terminated, remove the termination from others. Preferablly use cable supplied term(inator) power, so you can switch the end devices, like your Zip drive, off and have everything else still work.
> 
> If you have a mix of 8 bit and 16 bit SCSI on the same bus, it gets worse.

 

The Zip drive is connected with a small SCSI to DIN 25 cable. It has a DIN 25 connector for a daisy chain. The latter has a switch for active termination (on/off).

But there is one thing I wonder: the card has two connectors, one internal and one on its back. It is said there must be a terminator on both ends of a cable but most of the time there is only an internal cable (hence nothing connected to the back of the card). How is it supposed to work then?

Next you'll probably tell me to test the tape drive without the Zip connected, am I right? If I do, should I reboot the machine or is it Ok to do that on the fly? For now the orange led is flashing rapidly on the tape drive whatever I insert. I have no manual but I'm pretty sure it means "Problem".

As I read from technical data on the Internet, AVA 2904 is an 8-bit, 10 MB/sec fast SCSI-2 adapter. I've found back an old PDF data sheet about the tape drive. It looks like a Seagate Scorpion tape drive. It has an 8 bit data bus and can be switched to active termination.

Apparently both devices are 8 bit. Should I use the drive's active termination instead of the passive stub?

Now if the Zip drive is connected should I also use its active termination? I suppose the answer is yes?

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## NeddySeagoon

VinzC,

OK, you have a single 8 bit SCSI bus with three devices on, in order along the wire they are

Internal Tape drive, SCSI controller card, external Zip drive.

Active termination is supposed to give you better waveforms on the bus than passive termination. I can't say I could tell the difference on a 'scope. 

You need a termination on the tape drive, or at the end of the internal cable if the tape drive is not at the end.

You need a termination on the Zip drive, or on the end of the SCSI bus doing to the Zip drive, if the Zip drive is removed.

The controller card (in the middle) must not provide a terminator.

Both terminators must be present if you want amything on the bus to work.

SCSI is not normally (but can be) hot pluggable, so you must reboot when you reconfigure the SCSI bus.

The data sheet on your SCSI card says " Auto Termination Feature will enable/disable on board termination"

So if you disconnet the external part of your SCSI bus at the back if the card (no long lead to the Zip left connected), the card should look after the Zip comming and going. 

Your Tape Drive seems to be an ARCHIVE Model: Python 00095-001 but google wasn't very helpful beyond saying it was DDS-2.

Its always a good idea to add things to a SCSI chain one at a time - then you know what makes it break.

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## m_sqrd

Most adaptec card a a boot/config option (when the system post exstend BIOS info)

it will put up a message like pres ctrl-a to configure.

it look like the card is set to do auto termantion so it well sence the if there is a device chain on both connecters and configure it self for that. so you need to terminat the at the device(s).

and look like they are from you dmesg post. the flasing LED can a hardware error or even the drive telling you it needs to be cleaned with a cleaning tape.

the first thing I'd do is talk to the drive try

mt -f /dev/st0 status

and see if it gives you an error or what.

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## VinzC

Ok. Thanks a lot. I'm dismounting the PC and back right afterwards. I'll try active termination on the tape drive first.

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## VinzC

```
# tapeinfo -f /dev/st0

... I/O error
```

Drive removed. I'm pissed off  :Evil or Very Mad:  . The more I try to make it work the less it does. I've been trying to make that shit work for two years in vain. I've cleaned the drive over and over and over again, no way. Orange led is flashing after I insert any tape.

Thanks to all anyway for your help.

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## NeddySeagoon

VinzC,

You been using the right class of tape ?

DDS-2 and DDS-1 will be OK. Higher numbers won't be.

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## VinzC

 *m_sqrd wrote:*   

> Most adaptec card a a boot/config option (when the system post exstend BIOS info)
> 
> it will put up a message like pres ctrl-a to configure.

 

No, the card has no BIOS installed.

 *m_sqrd wrote:*   

> it look like the card is set to do auto termantion so it well sence the if there is a device chain on both connecters and configure it self for that. so you need to terminat the at the device(s).
> 
> and look like they are from you dmesg post. the flasing LED can a hardware error or even the drive telling you it needs to be cleaned with a cleaning tape.
> 
> the first thing I'd do is talk to the drive try
> ...

 

Yes, the flashing LED indicates a hardware error. After cleaning and cleaning all over again I decided to get rid of the tape drive. After all, it costed me nothing for it was given to me by an ex IT colleague when I worked at his company five years ago. I've never succeeded in having it work properly, neither under Windows nor Linux.

Full stop.

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## VinzC

 *NeddySeagoon wrote:*   

> VinzC,
> 
> You been using the right class of tape ?
> 
> DDS-2 and DDS-1 will be OK. Higher numbers won't be.

 

Yes, I only have DDS-1 and a few DDS-2.

EDIT: at least the Zip drive is working perfectly. And I've bought it. <relief/>

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## Mark Clegg

Not sure if this is relevant, but I'll throw it in the pot and let you decide...

Something is nagging me about Iomega doing their own SCSI card for the ZIP drive, and it was butchered to ONLY work with ZIP drives. A quick google tends to indicate that this was the Adaptec 1502, but it may be that the 2904 was used as well.

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## NeddySeagoon

Mark Clegg,

Lots of crippled SCSI cards were produced like this, so the cards would only support a single device,

I have one for a scanner that does not support interrupts, so its very slow with a SCSI disk. However, the other way round - device with fully functional SCSI card, I think was always OK.

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## VinzC

I care much of what you said but is there any communication between the SCSI card and a (my) tape drive when a cassette is inserted? Could it be that the card produces the (insert) error on the drive itself? If so what kind of SCSI card would be best for both the Zip and tape drive?

----------

