Need help understanding my new SCSI equipment

[CestusGW]

Allow me to make the usual formal declaration: I'm a total SCSI n00bie.

In any case, I recently had a string of really good luck. Some friends of mine found a (working!) Kayak XU800 workstation by the side of the road. It has an Adaptec 7892 chipset onboard for doing SCSI. So with that knowledge in mind, I set out to acquire some SCSI drives. One eBay auction later, I had an assortment of 10 old Quantum SCSI HDDs. I then also acquired an old 3U rackmount with 7 SCSI HDDs, and an external SCSI cable.

I'm now running into the issue of what on earth will work with what! I think I've got devices using 5 different SCSI acronyms all at once, and I have no idea how they all play together :( So here is my complete, unabridged inventory: can someone please tell me what goes with what, what can't go with what, and what bits and pieces I'll need to make everything go with everything?

The inventory:
Adaptec 7892 chipset with one internal SCSI header and one external SCSI header. From everything I've read, the connectors I have with this are Ultra160 SCSI. I understand this to be a synonym for Ultra2 SCSI LVD. In any case, the connector heads are both for 68 pin cables.
One 68 pin external SCSI cable (it has two heads, and is male-to-male)
Two Quantum Atlas 2 SCSI drives. These drives have 68 pin connectors. According to documentation, they are "Ultra SCSI 3" devices. The model number is 2275S.
One Quantum Fireball TM SCSI drive. This one again claims to be Ultra SCSI 3, and has a 50 pin (narrow?) connector. It goes by the model number "1.2S, 2.1S, 3.2S" [sic] That's literally how it's labelled.
7 Quantum Fireball ST SCSI drives. Again, claims to be Ultra SCSI 3 and shows model numbers "2.1S, 3.2S, 4.3S, 6.4S" Has a 50 pin (narrow?) connector
One Quantum Empire 1080D SCSI drive. This drive is actually a proprietary part manufactured for HP ... Maxtor doesn't list this as a valid Quantum model. It has a 68 pin connector on it, and I think it was listed as "Fast Wide SCSI 2" interface.
6 Seagate barracuda SCSI drives. Model number: ST15150WD. They are each 4.2Gb in size.
Two Quantum Atlas II SCSI drives. These have 68 pin connectors, and claim to be Ultra SCSI 3.
One 8 device (10 head) 68 pin SCSI cable.
One terminator which fits on the 68 pin cable.

Got all that? It took me several hours of research over PDFs and spec sheets to dig all that up, yet still I am confused.

Here's some questions:
Is there a difference between Fast SCSI and Ultra SCSI?
What type is my terminator? The terminator was functional for terminating the barracuda drives (which were in the rack mount along with the empire drive). Is it an active terminator, or passive?
I know that wide SCSI (68 pin) is differential, and that there are two flavours of differential SCSI: HVD and LVD. Are my drives HVD or LVD? I can't find that info anywhere. Can I get HVD drives to play nice with my LVD controller? If I jumper my HVD devices to work as "narrow" devices, will that work?
Are my 50-pin devices "single-ended"? What does "single-ended" mean"? I kept seeing that term on the Internet, but have no idea what it meant and never found an explanation.
I have more drives than I know my controller will support (it only does 15). If I get an add-on card, what flavour of SCSI should it be?
Can I adapt a 50 pin device to hook up to 68 pin cable? I've seen adapters for this on the internet, so it should be doable.

So yeah, I'm confused. Do I have LVD or HVD stuff? Can it self-terminate, or do I need to use the terminator I've got? Will the terminator I've got work?

I can't believe I went over the entire SCSI faq (http://h000625f788f5.ne.client2.attbi.com/scsi_faq/scsifaq.html), all of my products datasheets, and as many web posts as I could for several hours, only to come away confused. SCSI needs a swift kick in the butt for being so convulted :(

[starhawk]

yeah... it is wierd.

[animeguru]

I'm still learning myself, but I can answer a couple of your questions, so that's something...

Can I get HVD drives to play nice with my LVD controller?
Most certainly not. Using LVD and HVD equipment on the wrong card will probably fry the equipment. They use different voltage levels across the cable for the signal, and since one is "High Voltage Differential" and one is "Low Voltage Differential." I think you can understand why it could cause a problem. You can use them both in one system, but you'd need an HVD adapter card for the HVD equipment and an LVD (just about everything else on the planet) adapter card for the other drives.



What does "single-ended" mean"? I kept seeing that term on the Internet, but have no idea what it meant and never found an explanation.
Okay, why you've got a SCSI card, a lot of times there will be both an internal and an external connector. Most of the time they are actually on the same channel, so your 15 drive support is shared between the two. If you're using LVD, you can connect up to 15 drives between the two connectors in whatever manner you want... 10 internal and 5 external, 7 and 8, etc. With SE (single ended) SCSI, you can only use one or the other. The adapter card cannot be in the middle of the "bus" for timing and signaling reasons. (the bus basically being the cable). As such, if you're got SE drives connected to the internal connector of channel 1, you can't connect any to the external connector of channel 1. Thus there are only devices on one end of the bus.



Can I adapt a 50 pin device to hook up to 68 pin cable? I've seen adapters for this on the internet, so it should be doable.
In theory, yes but keep in mind that all of the drives on the same bus as the 50pin will be dragged down to that transfer speed. So if you've got some U160 drives (160Mbps) and some Ultra 2 (80Mbps??) on the same bus, everything will work at Ultra 2 speeds.


I hope that all helps some. IIRC that info is correct. Of course, like I said, I'm still learning myself, so if I've got something wrong, someone please step in and LMK. :p

[UICompE02]

Okay, why you've got a SCSI card, a lot of times there will be both an internal and an external connector. Most of the time they are actually on the same channel, so your 15 drive support is shared between the two. If you're using LVD, you can connect up to 15 drives between the two connectors in whatever manner you want... 10 internal and 5 external, 7 and 8, etc. With SE (single ended) SCSI, you can only use one or the other. The adapter card cannot be in the middle of the "bus" for timing and signaling reasons. (the bus basically being the cable). As such, if you're got SE drives connected to the internal connector of channel 1, you can't connect any to the external connector of channel 1. Thus there are only devices on one end of the bus.

This is incorrect. Single Ended and Low Voltage Differential refer to the number of wires used to transmit each signal on the bus. A Single Ended SCSI bus uses one wire for each of the signals, an LVD bus uses two wires to transmit each signal. LVD is better for long distances and high speeds because it uses the difference of the two signal levels rather than just one signal level to determine whether the data is a 0 or a 1. This means LVD is less prone interference since any interference will (hopefully) affect both wires equally and not affect the voltage difference between the two.

With SE and LVD buses, as long as the adapter card has the right connectors, the controller can be anywhere in the middle of the bus or on either end.

[CestusGW]

Alright, after doing some more reading, I have determined (finally):

If I hook up an HVD drive to an LVD bus, the LVD bus will shutdown (no frying/badness as others have implied).
If I hook up an LVD drive (which I don't have) to an HVD bus (which I don't have), the LVD drive will shutdown (wihtout damaging/frying badness)
LVD and HVD are both backwards compatible to SE SCSI. So if I jumper my HVD drives to act as SE (narrow) drives, then my LVD bus will throttle itself down to act like a narrow SCSI bus and everything will play nice.

So I've come to the conclusion that LVD and HVD was an unusual fork in SCSI where backwards compatibility didn't happen. So given my current situation with my associated drives, here is my plan:
Attach the narrow drives to my Ultra160 bus using a 50 to 68 pin adapter, and add the 1gig Empire drive to that as well.
Buy an old HVD PCI or PCI-X SCSI host card to run my barracudas, and the two Atlas II drives inside my drive enclosure.

As for my terminator (I have yet to hear anything on this subject): If it was physically at the end of the bus serving the barracudas, then I'm taken to mean that this was an active terminator for HVD SCSI, which is different from LVD SCSI, so this terminator will only work for an HVD bus.

[animeguru]

... With SE and LVD buses, as long as the adapter card has the right connectors, the controller can be anywhere in the middle of the bus or on either end.


I did not know that. I'll file that bit of info away for the future. Thanks for the heads up.


Makes a bit more sense... I always thought my "reason" seemed strange, but I've seen some crazy stuff about computer standards before, so I was willing to believe it! :p

[UICompE02]

Some HVD drives will not run in SE mode. I'm not sure which models that is true with, but I think it's mostly tape drives. Funny thing is, I've seen about 1,000 different SCSI devices in my life, but have never come across an HVD device, I wonder where your drives came from!

One thing to watch out for is that certain SCSI controllers may have an undocumented "feature" that will cause problems when you plug an HVD device into an LVD/SE bus/controller. Most LVD/SE controllers will go into a high impedance state when an HVD device is connected (high impedance is about the equivalent of an electrical disconnect), but there are some out there on the market that will get all confused and possibly fry components. I'm not exactly sure which ones these are, but I think you have the right idea with getting a separate HVD-specific controller for those HVD devices.

[UICompE02]

As for my terminator (I have yet to hear anything on this subject): If it was physically at the end of the bus serving the barracudas, then I'm taken to mean that this was an active terminator for HVD SCSI, which is different from LVD SCSI, so this terminator will only work for an HVD bus.

That is probably correct. There are basically three types of terminators that I've seen. SE, LVD/SE, and HVD. The HVD terminator will only work on an HVD bus. (I think you ahve seen now that HVD is kind of an oddity in the SCSI world...)

I recommend always using an active terminator. There is a certain speed level where you can use a passive terminator below that, but I think that is SCSI-2 and slower (but I can't remember for sure) So, just to be safe, always use an active terminator.

[UICompE02]

yeah... it is wierd.

I prefer the word "charming" :) But wait for the next generation, Serial Attached SCSI will get rid of a lot of this stuff that's been in there since SCSI was invented more than 20 years ago. It's kind of like a fresh start, the buses, cables, and topologies are much simpler (And no more external termination is required - one thing many new SCSI users have troubles with)

Of course SAS isn't without it's quirks, now we get to deal with expanders, wide ports, and crossover cables, etc.

[CestusGW]

hmmm .... wait for this new technology to roll out - it changes a lot, but it fixes a whole bunch of problems so everything should just be better!

Looks at IDE
Looks at SATA
Looks at IDE again
Looks at SATA again


You know, that sounds really familiar .... better the quirks, silliness and incompatibilities you do know than the ones you don't XD

PS: Thanks for all of your help ... I'm still finding SCSI confusing, but I guess that's because I'm trying to understand all 20 years of SCSI evolution all at once with a large batch of unknown hardware :)

[animeguru]

Funny thing is, I've seen about 1,000 different SCSI devices in my life, but have never come across an HVD device, I wonder where your drives came from!

Older Sun storage arrays. I know the A1000 and D1000 are HVD devices (I've got a couple), so I've got them hanging off of an HVD adapter card.

But I will say that they're the only HVD devices I've ever seen either.

[starhawk]

I prefer the word "charming" :) But wait for the next generation, Serial Attached SCSI will get rid of a lot of this stuff that's been in there since SCSI was invented more than 20 years ago. It's kind of like a fresh start, the buses, cables, and topologies are much simpler (And no more external termination is required - one thing many new SCSI users have troubles with)

Of course SAS isn't without it's quirks, now we get to deal with expanders, wide ports, and crossover cables, etc.

i still prefer things the way they are now: sata for hdd's, eide for other drives, and let's not forget usb, ieee 1394a/b (firewire), 9mdb serial ports, and, oh yes, the good old 25fdb parallel port, which still has some uses (zip drives and the like).

[CestusGW]

The HVD SCSI stuff came from an old disk array used at a scientific firm and an as-is grab bag off e-bay (just to let people know :) )

So I'm not really sure how I got 'lucky' enough to end up with purely HVD or narrow SCSI drives either :P

[UICompE02]

i still prefer things the way they are now: sata for hdd's, eide for other drives, and let's not forget usb, ieee 1394a/b (firewire), 9mdb serial ports, and, oh yes, the good old 25fdb parallel port, which still has some uses (zip drives and the like).

Well, Serial Attached SCSI will help out with that mess a little bit; you can plug SAS and SATA devices into the same controller!

[CestusGW]

I'd prefer having everything inside my PC case go to SATA over EIDE just because of the ergonomics of it all. But I hear you - I like still having my USB, parallel, serial, SCSI etc. available because you never know when you might need it. Every PC I own for the next ten years is still probably going to have a floppy drive :D

[starhawk]

same here with the floppy... tho i'm pretty sure that cdroms and the like aren't gonna be sata for a while yet... but we'll see.