Configuring a SCSI CD-Rom

[no_fat_chicks]

I recently transferred a working SCSI cd-rom from one PC to another & didnt change any configuration in the setup utility as it worked fine w/o it.

I have since had a call from the customer who says Windows98 is now hanging at the 'hit ctrl-A to enter SCSI setup utility' message that comes up during post whereas it used to stop there for a couple of seconds then continue to load windows. He said it started to hang at this message so he would simply reboot & it would go past it, but it has got progressively worse to the point it wont go past it at all. I assume he may have entered it & not knowing what to do, changed something.

The SCSI drive is an adaptec which I understand can be a bit easier to configure than most. Should it simply be a matter of perhaps resetting the IRQ or do I need to do something else as well as I remember there was another settings field I could change in the utility as well?

[HAL9000]

If you suspect that he changed something in the SCSI BIOS, just enter the SCSI BIOS and reset the defaults. There shouldn't be anything set differently.

[Toaster]

Howdy,
Just a suggestion, SCSI CDROM drives offer the best performance hard set to SCSI ID-6 or the highest practical ID. It sounds as though the controller is set to "SCAM" or SCSI Configured AutoMatically.
I perfer to hard set ID's and use active termination.
Higher ID's give higher priority.
Termination is KEY to SCSI performance and reliability.
You didn't specify adaptor type or CD model, hard to help from there.

[no_fat_chicks]

Ok-thx.

I know the SCSI is an Adaptec thats all..its one I refitted for a customer.

Anyway, no problem, I know the device had a rather loose fitting cable where it fits to the motherbaord & I'm not sure the customer hasnt meddled with things so it may just need a new cable & to reset the configuration so I may not actually need to change anything. If I do need to change the auto settings what ID should I select? It only has the one SCSI device fitted.

[Toaster]

Howdy,
If its the only device on the SCSI bus, enable termination, make certain that the drive is on the end of the cable and set the ID to 6.
Any ID from 0-6 will work so long as that ID is not in use by another device.

[no_fat_chicks]

Ok. It is the only SCSI device on the BUS & termination is already enabled as it was used on another PC before & was the only device.

Thanks for your help.

[Floppyman]

Originally posted by Toaster Howdy, Just a suggestion, SCSI CDROM drives offer the best performance hard set to SCSI ID-6 or the highest practical ID. It sounds as though the controller is set to "SCAM" or SCSI Configured AutoMatically. I perfer to hard set ID's and use active termination. Higher ID's give higher priority. Termination is KEY to SCSI performance and reliability. You didn't specify adaptor type or CD model, hard to help from there.

Hi Toaster,

I also use SCSI and I hadn't heard that before. Why do you say it offers best performance on ID 6? Also say I had 2 hdd's and 3 cdroms, the adapter itself uses ID 7 (I think). Would it be best to put hdd's on ID0 and ID 1 and the cdroms on ID 4,5,6, respectively, or would you do it differently (example set the hdd's on a higher ID???). Thanks in Advance!

[Toaster]

Hello Flopster,
The SCSI bus is a "prioritized" bus.
That is, the higher the address, the higher the priority. (see notes)
Almost all devices have a "disconnect" option that is very often set to "enable disconnect". This allows "busy" devices to disconnect from the SCSI bus so other devices can use "master" the bus. NEVER disable "disconnect" except in very few circumstance. (some scanners and early CDROM drives)
Most host adaptors (your SCSI card, referred to as HA) default to device 7, leave this as is at ID 7.
The lowest SCSI ID will be the "bootable" device IF the device is an "80h" device.
(80h is a system I/O interupt pertaining to the 1st. HDD)
So, the hard-disk with the lowest SCSI ID is the "boot" device/drive.
CDROM drives are substantially slower then hard-disks and thus need more time on the bus. To give these devices more time, assign a higher ID.
SCSI HDDs often are set from "low to high" and "other" devices are set "high to low".
The improvement is actually minimal UNTIL several devices are active. When several devices are active, the HA gives SCSI bus priority to the device with the highest SCSI ID. In this case, the CDROM/Writer becomes active and thus requires more time on the bus. The HDDs "disconnect" from the bus so the CDROM drive(s) have more time. When the HDDs need time, the HA allows the HDDs to become active and allows them more time on the bus.
A "busy" HA (several attached and active devices) could take too much time from the HDDs and thus reduce throughput if say 2 CDROM/Writer devices were "active" and the HDD were active at the same time. This is the reason why its better to have multiple HA's, one for HDD needs and one for slower devices such as CDROM/Writers and other floptical or tape needs.


Note:
Wide HA's still set ID 7 as the highest priority even though IDs exist to device ID 15. That is....
Device ID "priority" goes from device ID 7 (HA) to device 0 and from Device 7 to device 15. Device 7 is the highest priority.
So, to go a bit further to "enhance" performance under heavy multitasking use, one could set the HDDs as devices 5 and 6 and a second HA for "other" devices with the selects set at 5 and 6. The lowest ID (HDD) is the "boot" device.
A HDD DOES NOT have to be set to ID "0" but it keeps things simple for those that don't fully understand the SCSI bus. Simple rule is that the LOWEST ID setting for an HDD WILL be the boot device.
Many HA's (including Adaptec 2940 series and most others) allow via the SCSI BIOS the ability for the user to select the "boot from SCSI ID-X". This is often used to "boot" other O/S's.
Example:
Devices 0 and 1 are HDDs. "Boot from" ID is set to device "0" as default.
Selecting "boot from" device to "1" allows the HA to boot from the alternate ID.


In the workstation world, the SCSI HA is often set as device "0" and the system HDD is set to device "7". This gives the HDD the "highest" priority and thus the most amount of time on the bus.


Notes to the note:
Users who have BOTH SE (single ended) *and* LVD (low voltage differential) devices on the SAME HA will FORCE the LVD device to run at SE data rates.
This in effect forces LVD devices into "SE" mode reducing throughput.
If this is the case, 2 HAs are the best option, one for LVD devices *ONLY* and one for SE devices *ONLY*.
Under IDEAL conditions for full utilization of the SCSI bus, HA-1 (host adaptor 1) is an LVD capable HA and thus ONLY runs LVD devices. HA-2 runs all SE devices.
All devices (LVD and SE) use ACTIVE termination. LVD and SE terminators are DIFFERENT. Usinf an SE terminator on an LVD device forces SE mode.

At least one device on each HA should be set to "provide" TERM power. More then one device may provide TERM power but at least one MUST.

The *IDEAL* set-up:
HA-1 set as ID-0, HDD-0 is set to ID-7, HDD-1 is set to ID-6 and so on.
HA-2 set as ID-0, CD/RW set to ID-7, CD set to ID-6 and so on.

"Except"
Some HA will NOT allow the HA to be set for anything other then "7".
Most allow the HA ID to be set to any valid value.
(Adaptec 294x, 2916x, BusLogic, Qlogic and many others)
Your HA "must" have a BIOS to use these settings (easily) though there are other ways for cards without BIOS.

[no_fat_chicks]

Ok, the outcome of this is an odd one.

I checked the cabling for the SCSI first & it seemed fine. I then checked the BIOS settings & nothing appeared to have changed.

I then booted up Win98 & it got past the SCSI config utility prompt & all was fine. Device manager was ok too.

Dunno..