SCSI drives running slow. Why? Help!

[SuperPickle]

Alright, I've been running a SCSI HDD for a while now and it's been totally cool. I recently decided to get a SCSI burner and CD-ROM, and now everything went to hell.

Adptec 29160N adapter ID 7
HDD ID 8 bus 16
Burner ID 3 bus 8
CD-ROM ID 5 bus 16
The Plex CD-ROM is Wide and my HDD is U160, both 68pin and on the same 5 device (6 position) LVD cable terminated at the far end. Neither drives have its internal terminator jumper set. My burner is 50pin and on its own cable.

The computer sees all the drives fine and they work, however the HDD's sync is now down to 40 where it should be 160.

According to Gayr Field's SCSI Faqs, "Some people have the idea that attaching a SCSI-1 device to a SCSI-2 bus will cause the entire bus to run at SCSI-1 speeds. This is not true"

What am I doing wrong, or am I SOL? Thanks for any imput.

 

[bozo1]

While that statement holds true for SCSI-1 vs. SCSI-2, it does not hold true for LVD drives and non-LVD drives. You need the Ultra160 drive on its own bus.

 

[SuperPickle]

Damn. I was hoping that wan't the case. Would getting a 50pin->68pin adapter fix the issue and have both opticals running on the same 50pin cable (if even there is such an adapter)? Thanks

 

[bozo1]

There are adapters but you'll lose the 'wide' feature. I doubt you'd notice the difference as the drive speed will be the limiting factor. Hypermicro has them for $19 which sounds a little steep for something like that so you may be able to find it cheaper elsewhere.

 

[JeffreyLebowski]

Originally posted by: bozo1
While that statement holds true for SCSI-1 vs. SCSI-2, it does not hold true for LVD drives and non-LVD drives. You need the Ultra160 drive on its own bus.

Ding ding ding, here you go.

 

[SuperPickle]

Thanks for the help. Now my grand visions of SCSI-lovin' are reduced to mere SCSI-likin'. Time for some more hardware shopping.

 

[bozo1]

The 29160 (no 'n') would have been a better choice for you. LVD, 68-pin ultra-wide, and 50-pin ultra connectors. Everyone would be happy.

 

[SuperPickle]

Hmm...I have a good buddy that has that card. I wonder if he'd be willing to give that one up? Even swap? Thanks again.

 

[dszd0g]

People have tracked down your main issue. LVD is a differential signal (uses a pair of wires to send the signal) vs. single ended which uses a single wire vs. ground (well both wires still exist, but one is grounded). A SE signals and LVD signals cannot coexist.

From The Book of SCSI 2nd Edition:

As a result, LVD devices go by the Voltage they see on the DIFF SENSE signal to decide whether any single-ended devices are present. If the Voltage is less than .6V, there are single-ended devices; if it's between .7V and 1.9V, it's all LVD; and if it's over 2.2 V, there are HVD devices present. If HVD devices are present, the LVD device shuts off its bus drivers to avoid damage.

Next, your HDD should be on SCSI Id 0 (or 1, but for cleanliness I would go 0). Your Burner should be on ID 6 and your CD Rom should be on ID 5. Although really the only thing that is important is that the SCSI is that when using all Ids less than 7 (the rules change above 7), the hds should have the lowest, cd drives next, tape drives after, then burners. The slowest devices need the highest priorities otherwise they may fail to arbitrate for the bus. This is especially important for burners as they need the data when they want it, by giving the burner the highest priority it gets the data when it wants it.

You need the 29160(not N) which has another segment or the 39160, which has two entirely seperate channels. The Plextor Burner is wide, but is it LVD (I doubt it). Putting that on the same cable as the HD will prevent the HD from going into LVD mode. The 29160 has two 68-pin connectors, 1 LVD one Ultra Wide.

Normally one wouldn't be able to Y a SCSI bus (have it go in three directions on a single channel), but Adaptec does some electrical isolation (segmenting) to create multiple SCSI buses, so this is not an issue on the 29160 card. Check their documentation for proper termination in this situation, I believe one would terminate at the burner on the Ultra/Wide segment, at the CD-ROM on the narrow segment, at the end of LVD segment with an active LVD terminator, no termination on the Ultra/Wide narrow segment on the card, termination on the LVD segment of the card (the card you should be able to set to Auto to do this for you). That way both segments would be terminated in two places (The SCSI bus needs to terminated at both ends, an end may be the card).

 

[dszd0g]

For now make sure to terminate your CD-ROM drive or have a terminator on the end of the 50-pin cable (Terminating the CD-ROM is just fine).
If you don't need the burner you can unplug it and the LVD segment should return to full speed.

 

[SuperPickle]

dszd0g
I had little idea that the SCSI ID's were prioritized as such but in thinking about it, one would think it only logical to be as such. I can change the IDs and will do so, but had no need to do that before as the only SCSI device I had in my system was the HDD so it wasn't an issue. I also understand that my CD-ROM and HDD can't coexist on the same cable lest my HDD lose LVD. In a perfect world, the burner would rest on the narrow shelf, the CD-ROM on the wide shelf, and the HDD on the LVD shelf. I don't know if this is even possible with my current hardware (adapter). Unfortunately, I'm not going to run and upgrade my card just to get this CD-ROM to work as designed. Is my best and cheapest way to get the most, albeit not necessarily optimal performance out of all parties involed to get an adapter to put put both opticals on the 50pin bus? If I lose the wide aspect of the drive, so be it as it's better to lose that than to downgrade my HDD from a 160 sync to 40 sync. I fear my biggest faux pas was to get a 68pin CD-ROM but getting a cable adapter and losing some features is better than paying much more for another drive and having this one lay useless or getting a new controller.

I am humbled by this experience and while I'm an enthusiest, I'm far from a guru and let this be an example to others that are brave and performance hungry that want to delve into the SCSI world--do your homework before jumping on a good deal. It might bite you in the ass.
Thanks to all for the ego-crushing, but indispensable information.

 

[dszd0g]

Could you please distinguish somehow between your CD-ROM and your CD-R(W?) burner? Calling both CD-ROM in your last post makes it a little difficult to follow which you are talking about.

What model is the burner? What modes does it support Fast(-10), Ultra (Fast-20)?

Synchronous Narrow (50-pin):
SCSI-I/II - 5MB/s
Fast (Fast-10) - 10MB/s.
Ultra (Fast-20) - 20MB/s.

Even the 5MB/s is 34X as far as CDs go. So as long as it's got at least Fast you should be running the burner at max sustained speed, the only difference will be in the bursts. If you can't return the burner or come up with some trade with someone, I would go the burner 68pin->50pin adapter route too.

 

[SuperPickle]

Just for sake of clarification to those of you have been following this lament:
Burner is a 50pin Yamaha 8x4x24 CD-RW that supports a 20M/s sync
CD-ROM drive is a 68pin Plextor 40-TW (I think) 40x drive that supports 40M/s sync
HDD is an IBM Ultrastar 18GB 10K 68pin U160
My plan is to find an adapter that will let me plug my Plex into the 50pin garage on my card as well as the Yamaha burner on the same cable keeping the HDD freewheeling on it?s own LVD cable. If any reading this has one (the adapter) they want to get rid of, let me know.

 

[Woodie]

I believe (please correct me if I'm wrong) that you cannot connect a 68-pin device to a 50 pin controller (channel). The controller must be "greater than or equal" to the devices. So, you can get adapters that let you connect a 50pin device (CD) to a 68pin cable, but not the other way 'round.

You should be able to trade your 68pin burner for a 50 pin burner or trade the controller for a multi-channel.

Matter of fact, I have a 50 pin HP burner that I'd be willing to trade (with some $$) for your wide drive, if that's the way you decide to go.

 

[dszd0g]

Originally posted by: Woodie
I believe (please correct me if I'm wrong) that you cannot connect a 68-pin device to a 50 pin controller (channel). The controller must be "greater than or equal" to the devices. So, you can get adapters that let you connect a 50pin device (CD) to a 68pin cable, but not the other way 'round.

Nope, adapters are available. I have no idea if the one I linked to is a good one or not, just that they do exist.

SCSI devices require a WIDE DATA TRANSFER extended message negotiation before they will transfer in wide mode. The host adapter shouldn't try to do a wide negotiation on the 50-pin channel and if the drive tries it, it will fail and remain in narrow mode.

 

[Need4Speed]

Originally posted by: Woodie
I believe (please correct me if I'm wrong) that you cannot connect a 68-pin device to a 50 pin controller (channel). The controller must be "greater than or equal" to the devices. So, you can get adapters that let you connect a 50pin device (CD) to a 68pin cable, but not the other way 'round.

You should be able to trade your 68pin burner for a 50 pin burner or trade the controller for a multi-channel.

Matter of fact, I have a 50 pin HP burner that I'd be willing to trade (with some $$) for your wide drive, if that's the way you decide to go.

mmmmm...not true...SCA for instance is 80 pin down yo 68.

 

[Woodie]

80 pin doesn't count...that's a hardware spec that includes Wide transfer + power.

I'll stand corrected on the wide device on a narrow chain. I've been unable to make it work, and that's been confirmed by the work hardware gurus. I have a wide chain with both narrow and wide devices. (narrow one towards the end, and wide one closer to the controller.)

I'm still a little credulous...I'll have to go do some more research and post back.

 

[dszd0g]

Woodie, what kind of adapter are you using? What kind of termination does it do?

 

[Need4Speed]

Dont Some Adaptec Cards using SpeedFlex allow mixed devices to co-exist on the same chain?

 

[dszd0g]

Originally posted by: Need4Speed
Dont Some Adaptec Cards using SpeedFlex allow mixed devices to co-exist on the same chain?

Yes. You can mix Fast (Fast-10) and Ultra (Fast-20). You can mix Ultra2 (Fast-30) and Ultra160 (Fast-40). But you can't mix SE (Fast-20 and below) and LVD (Fast-30 and above) otherwise everything runs SE. You can mix narrow and wide on the same bus segment too (as long as it is all SE). Some older host adapters if one ran narrow and wide on the same segment it would drop everything to narrow. Some older host adapters would drop to the speed of the slowest device. That is part of what SpeedFlex is for. However, all that is in the SCSI specification and IMO SpeedFlex is mainly marketing. Other companies do the same thing without SpeedFlex.

However, what I haven't seen other companies do is segment the SCSI bus. That is Adaptec's proprietary part of SpeedFlex. Other companies use multiple channels to obtain the same results, but Adaptec cards single channel cards can have an LVD segment and an SE segment, like the 29160 and 29160N. The 29160N has the narrow (internal and external) SE segment and the wide LVD segment. The 29160 has a narrow and wide SE segment, and a wide LVD (internal and external) segment. Notice how each of the segments can have two connections to it if one takes into account the external, this prevents Y ing of the SCSI bus. However, this segmenting of the SCSI bus does add overhead as the host adapter does have to combine the two segments in the controller and allow for communication between the two segments (they are technically on the same SCSI chain and must be able to talk to each other with the SCSI SPC and CAM protocols).

 

[Woodie]

I have a fast/wide Mylex controller (RAID actually).

Externally, the hard drive cage provides fast/wide termination. Channel 0.
Internally (CD+CDRW) I use a wide ribbon cable, with a terminator on the last connector. Channel 1.

edit: Channel info

 

[dszd0g]

Originally posted by: Woodie

Externally, the hard drive cage provides fast/wide termination. Channel 0.
Internally (CD+CDRW) I use a wide ribbon cable, with a terminator on the last connector. Channel 1.

Where is the wide device(s) on the narrow channel that you are having issues with? You said you were having issues with wide devices on a narrow channel?

 

[Woodie]

Sorry for the confusion dszd0g, my system is working fine. I don't remember the hardware I was trying to get to work, I know it was on another system...

I think this was the scenario:
Adaptec narrow controller...f/w Seagate HD...narrow IBM CD...terminator
I think the cable was a narrow one, with an adapter for the HD. Or it might have been a wide cable, with adapters for the controller and the CD.

Here's some info from Adaptec:
"Please note that in order to mix wide and narrow devices, a wide host adapter (2740W, 2742W, 2744W, 2940W, 2940UW Mac, 2944W, 2940UW, 3940W, 3940UW, 3940UW Mac, 3940UWD, 3944UWD) is required."

More Adaptec
(bottom of the page) "Yes...it will still work"

But, RamElectronics has this for sale
"*Ultra2/Ultra160 drives will need their "SE/LVD" jumpers set to "SE" in order to work with narrow SCSI."

So, clearly there is a way to connect Wide devices to a narrow scsi chain. But, you get a significant performance hit, and it will cost you $22.50 (for this particular adapter).