Mac Plus sees external HD, but won't boot from it

[bigmessowires]

I've been struggling to get my external HD to work with my Mac Plus. I thought it was a question of SCSI cable length, but I was wrong. I finally broke down and tried every possible permutation of SCSI termination settings, and found that the only way the Plus will see the HD is if there's a Zip drive in the middle of the chain, with the Zip's termination on and the HD's termination off. From this I concluded that neither the Plus nor the external HD are providing termination power, but the Zip drive does. But that's another problem for another day.

With the HD and Zip connected as described, the Plus can see the external HD and can mount it, and read/write files from it. But it won't boot from it-- it just sits at the question mark disk screen. This is after I copied the System Folder from another disk onto the HD, and double-checked that the external HD's folder showed the "blessed" icon. I also tried reformatting the HD with Lido 7.56 for good measure, but it didn't help.

Anyone have a guess about what kinds of things would cause a Plus to fail to boot from a disk that it's otherwise able to mount? All I can think of is that it might be some problem with the System file, or the disk driver, but I'm a little stumped as to what to try next.

 

[gilles]

What is the filesystem type of your external HD, also what is the size and SCSI ID?

I think there's a boot key to force boot on a specific SCSI ID.

 

[Byrd]

Does it boot up off the Zip drive? It could be the interleaving of the drive, try to format us using Apple's HD SC setup utility instead

 

[bigmessowires]

It's a 1 GB external HD, at SCSI Id 1. HD SC setup doesn't recognize it, since it's an IBM-made disk and not an Apple one. The HD was formatted for Mac OS with Lido 7.56. I can work with the HD fine after booting the computer from different disk.

The Plus boots fine off the Zip drive (SCSI 5).

Interleaving might be a possibility-- but I thought the wrong choice of interleave would cause poor performance, but not failure to work at all. If I had the wrong interleave, does it make sense that I'd be able to mount and use the HD later after booting from a different disk?

 

[Byrd]

Info I found here:

http://macfaq.org/hardware/harddisk.shtml

2.2.3 - Why won't my Mac Plus see the external HD I use with my other Macs?
The buffer on many older HDs is rather small, and the SCSI on the Mac Plus is quite slow. When these two factors are combined, it causes the HD to effectively be "too fast" for the Plus. To get around this, HDs for use with the Mac Plus were often formatted with a 3:1 interleave, which slowed down the data flying at the Plus enough so the Plus could handle it. If your external HD is an older unit and has only been used with Macs newer than the Plus, it probably has a 2:1 or 1:1 interleave and is too fast for the Plus. To remedy this, back up the HD and reformat it on the Plus (or on another Mac, as long as you can specify the interleave ratio). This will make the drive slow enough for the Plus (and probably won't impact its performance on other Macs too negatively). Most newer hard disks have enough cache so as to make interleave ratios irrelevant.

I just don't remember though if a Mac Plus can still read a SCSI hard disk when interleaved at a 1:1 ratio. I do find it interesting however the last sentence regarding using more modern drives (which you are running) that negate the need for interleaving due to their onboard cache. Certainly all the hard disks I've used on a Plus have been slower, original 20 - 40MB drives which did need interleaving. There is also information there regarding hacking HD SC setup to work with non-Apple drives.

JB

 

[bigmessowires]

I interpreted that last setence to mean that a 3:1 interleave won't negatively impact performance with a modern HD, thanks to its cache-- not that 3:1 interleaving isn't necessary for modern drives with a Mac Plus. Does that sentence even make sense?

I'll give the 3:1 interleave a try, since it should be a simple experiment. I still don't see how a bad choice of interleave would make the drive usable as a data disk but not a boot disk, though... mysteries.

 

[bigmessowires]

Interesting. If I try another other than 1:1 intervleave with Lido 7.56, the format immediately fails.

Those instructions for hacking HD SC Setup to recognize non-Apple drives only applies to HD SC Setup version 7.3.5, which I'm guessing is the System 7 version? I'm running System 6 on the Plus, and my copy of HD SC Setup doesn't even have the resource that's supposed to be edited.

I'll dig around some more...

 

[phreakout]

Bigmessowires,

Make sure that the SCSI ID for the external hard drive is set to ID #2, 5 or 6. Make sure you have the termination enabled through Zip drive, if you have it as the first device on the chain, or enable it on the HDD if you have that as the first device. Make sure also that the cable is a good one and not going to fail. It sounds like the drive has not been formatted, partitioned and a proper driver installed. So with that in mind, use Apple HD SC 7.3.5 (patched). You can find a copy of it on the System 6 Heaven website, Jag's House Memorial website, C C Adam's The Mac SE Support Page (http://www.ccadams.org/se/hard_disk.html) and Gamba's Home Page (http://home.earthlink.net/~gamba2/superbooter75.html).

The Mac Plus does need an interleave of 3:1, the SE 2:1, while all the other models after the SE use a 1:1 ratio. This is due to the fact that some early drives didn't have an internal data cache. If a drive DOES have a data cache, you can set the interleave to 1:1; otherwise, set it to 3:1 or 2:1, just to be safe.

You did the "blessing" process correctly, but it seems the drive just needs to have the proper driver installed. That can be done easily with the "patched" version of Apple HD SC 7.3.5. It recognizes MOST hard drives that aren't "Apple-branded".

Give that a try and report back your results.

73s de Phreakout. :rambo:

PS: If you need a copy of Apple HD SC 7.3.5, already patched, PM me and I can send it to you via email.

 

[bigmessowires]

Well folks, I'm at my wit's end here, and would appreciate any suggestions you have. I've now tried two different external hard drives, in two different enclosures, with three different low-level formatting utilities. In all cases I'm able to mount the drive and use it normally after booting from another disk. But if I attempt to boot from the external drive, the Mac Plus just sits at the flashing question mark screen. The drive has System 6.0.8 installed on it, and shows the "blessed" icon on the System Folder.

I've tried formatting with a hacked version of Apple HD SC Setup 7.5.3 (from another computer, since it won't run on a Plus), Lido 7.5.6, Blue Disk Manager, and MicroNet Utilties. I tried set the interleave to 3:1 in the utilities that let me specify, but I can't be certain it worked. MicroNet in particular let me set the interleave option to 3:1, but then still reports a 1:1 interleave when it formats the disk. All the utilities format the drive OK, and result in a usable data drive, but not a drive that will function to boot the Plus.

The two drives are an IBM 1GB and a Quantum 800MB.

A Mac Plus with an external hard drive is a pretty common animal, so I can't imagine why I'm having so much trouble with this. I feel I must have overlooked something basic.

 

[bigmessowires]

Could it be that the drive isn't mounting itself by default? Depending on which format utility I use, and what other disk I use to boot the Plus, sometimes the external drive won't appear on the desktop. But if I run a SCSI utility, I can see the drive and mount it.

 

[gilles]

there is some echo to this post on a french forum

http://silicium.org/forum/viewtopic.php?f=28&t=27478

with the same (un) success...

 

[bigmessowires]

Make sure you have the termination enabled through Zip drive, if you have it as the first device on the chain, or enable it on the HDD if you have that as the first device.

I'm not using the Zip drive now-- just an HD connected externally as the only SCSI device.

Make sure that the SCSI ID for the external hard drive is set to ID #2, 5 or 6.

Both drives I tried are set at 1, and there are no other SCSI devices. Is there something magic about the other IDs?

Make sure also that the cable is a good one and not going to fail.

Yup, tried two different cables, one 6 foot cable and one 2 foot cable.

It sounds like the drive has not been formatted, partitioned and a proper driver installed.

It has been formatted and initialized. Once mounted (after booting from another disk), I can use the external HD fine, and copy files from and to it without trouble.

The Mac Plus does need an interleave of 3:1, the SE 2:1, while all the other models after the SE use a 1:1 ratio. This is due to the fact that some early drives didn't have an internal data cache. If a drive DOES have a data cache, you can set the interleave to 1:1; otherwise, set it to 3:1 or 2:1, just to be safe.

At least one of the drives has a data cache, not sure about the other. I've tried to set the interleave using both Lido 7.56 and MicroNet Utilities, but it seems to ignore whatever interleave setting I request, and use 1:1.

You did the "blessing" process correctly, but it seems the drive just needs to have the proper driver installed. That can be done easily with the "patched" version of Apple HD SC 7.3.5. It recognizes MOST hard drives that aren't "Apple-branded".

I can't run HD SC 7.3.5 on the Plus, but I tried connecting the drive to a Power Mac 8500 and formatting it from there. The hacked 7.3.5 recognized the drive and formatted it, but it still won't functioning as a boot drive for the Plus. It mounts after booting, and I can copy files from and to it, but it won't work as a boot volume.

The external hard drive has System 6.0.8 installed on it, and shows the "blessed" icon on the System Folder, so I'm pretty sure the OS install is OK.

 

[PowerPup]

How about you try and install say Mac OS 7.5.3 on one of the external HDs and see if they boot from the 8500. That way we'll see if these drives are capable of doing so. Even though theoretically it should work.

 

[bigmessowires]

Good idea! Actually I can do an even better test: use a Mac LC II, and connect the external hard drive with the original System 6.0.8 install that I made for the Plus.

I did this test, and the LC II booted right up from the external HD. So that proves the drive is good, the cable is good, and the system software is good. It also proves the drive doesn't have some kind of magic "I am not a boot volume" or "don't mount me" flag set in its driver somewhere.

It seems the drive (I only tested one of the two) just has some fundamental Plus incompatibility, that allows it to be mounted and used after booting from another disk, but not used as a Plus boot volume. That's really weird, since I think it should either work all the time, or not at all. If the interleave or driver were somehow incompatible with the Plus, then I shouldn't be able to mount it and use it after booting from another disk, should I?

 

[bigmessowires]

One other test: I put an Apple-brand 40MB hard drive in one of my external enclosures, and the Plus boots from it OK. So it's something specific to the other drives that the Plus doesn't like. One is a 1GB IBM drive and the other is an 800MB Quantum drive.

 

[gilles]

even if it's not supposed to be a problem below 2Gb. Try a little system partition of 40Mb on this disc.

 

[bigmessowires]

I went back and formatted the 800MB drive again using Apple HD SC Setup 7.3.5 on the LC II, and partitioned it into a 40MB and 760MB partition. Installed the OS on the 40MB partition, and the Plus still won't boot from it.

I am so stumped by this one. :-(

 

[bigmessowires]

One more clue: I get different mounting behavior for the external HD, depending on what other disk I boot from:

If I boot from a vanilla 6.0.8 floppy, then the external HD will not be mounted or visible in the Finder after booting.

If I boot from a 6.0.8 floppy that also contains SCSI Probe and the Iomega driver (just the driver INIT, the actual Zip drive is not connected), then the external HD appears in the Finder after booting.

So it appears that one of either SCSI Probe or the Iomega driver is tickling the SCSI bus and detecting the external HD, in a way that the normal Mac startup routine doesn't.

 

[bigmessowires]

This is getting silly now... I decided to give up and just use the 40MB as the Plus boot drive, since I know that works at least. So I erased the LC-specific install of System 7.1 that was on the 40MB drive, and installed 6.0.8 instead. Now the Plus boots from the external 40MB, shows the happy mac icon, but dies at the "Wecleom to Macintosh" scrren. It's continuously redrawing the "Welcome to Macintosh" icon and text over and over, like it's in an infinite loop. Agrgh!!

WTB: one external hard drive with System 6 on it, known to work with the Mac Plus.