Can I use one of these SCSI adapters on the internal SCSI bus?

[tattar8]

I have a number of Macs with dead/dying/untrustworthy SCSI drives (IIx, IIsi, Q660AV, Q475, PM9600, SE, SE/30, Classic II), I don't want to get a SCSI2SD for each of them, and I have a ton of assorted SCSI drives lying around that are a good bit newer than 1990.  I was browsing eBay and came across these:

https://www.ebay.com/itm/SCSI-68Pin-68-Pin-Male-to-50Pin-50-Pin-Male-Adapter-Converter-CYN/233175965967?hash=item364a5ee10f:g:Yh4AAOSwkFZcIFce

https://www.ebay.com/itm/SCSI-SCA-80Pin-to-68Pin-to-50Pin-IDE-Hard-Disk-Adapter-Converter-slim-Card-Board/372511528024?epid=4021687196&hash=item56bb6ad458:g:Y24AAOSwHkBcd6ue

Will these Macs recognize drives connected through one of these, and if so, what's the largest hard drive they'll recognize (since most of my drives are in the 15gb range)?

 

[olePigeon]

I believe they should work.  If you're running an older computer with System 7.5.2 or older, then the largest partition is 2 GBs.  7.5.3 or newer is 4 GBs.  So for 15 GB drive you'll want to partition it into multiple partitions in sizes smaller than indicated.

For any Mac with PCI, it's up to 2 TBs per partition (except for IDE drives, where I think it's limited to 2 GBs on some models.)

 

[Cory5412]

They should, and with SCSI, if you have a new enough Mac and a new enough OS, it should be able to use essentially any size of SCSI device ever manufactured.

I've never used such an adapter so I can't vouch for that particular kind of adapter, but in general 50 to 68/80 and SCA adapters are known to work with Macs.

Reserve your largest drives for the 660 and 9600. SE and IIx you'll want to put your smallest drives in. The CII, SE/30 and Q475 should be able to run bigger disks with 7.6.1, but they're both short on cooling and space.

The list of  volume size limits is here: 

(except for IDE drives, where I think it's limited to 2 GBs on some models.)

I've never heard about this before. Do you know what models this is?

Some Beige G3s and related derivative platforms have like a weird 8 gig thing going on in some OS releases but otherwise I haven't ever seen anything about a 2-gig limit, unless that's like, an error with a particular PCI card? 

 

[olePigeon]

@Cory5412  I must be thinking about 8 GBs.  Rev A Beige G3 had an issue with it unless you replaced the VRM.

 

[tattar8]

So essentially I can use any disk I want regardless of size, but I just have to partition it into disks of up to 2GB?

Does this still hold true under A/UX?  I'm thinking of installing that on the IIx.

 

[olePigeon]

4 GBs if you're running 7.5.3 or newer.  2 TBs for your PowerMac 9600.

I don't know much about A/UX, so I couldn't say.  It's a Macintosh IIx, so, probably safe to just assume 2 GBs because you're unlikely to fill anything that big.

 

[Cory5412]

Rev A Beige G3 had an issue with it unless you replaced the VRM.

That's also not how I remember it, it was an issue with the actual controller and/or the firmware, what would the VRM have to do with IDE access?

4 GBs if you're running 7.5.3 or newer.  2 TBs for your PowerMac 9600.

7.6.1 and SCSI manager 4.3 is what gets you 2TB, all 040s save PowerBooks and the 630 should be able to do that.

 

[olePigeon]

That's also not how I remember it, it was an issue with the actual controller and/or the firmware, what would the VRM have to do with IDE access?

Because I'm an idiot and getting 2 different things mixed up.  I owned a Beige G3 and went through multiple steps to get the HDD and the CPU working.  I ended up replacing the VRM so I could upgrade the CPU.  It had nothing to do with the HDD.  I'm just not thinking very straight lately.  I need to stop and read what I'm writing before I post it.

 

[Cory5412]

Ah, no problem! I just wanted to make sure, because I was like "this seems weird."

 

[jupo]

I'm curious if anyone here has direct experience with SCA drives and on what systems.

I have had limited success with SCA (80-pin) drives in my setups, except on relatively recent (G3 era) systems. The first obstacle is that they have no circuitry for termination on the drives - they are designed to be plugged into a bus that has active termination at the end, even on an internal chain. I have not yet acquired any internal terminators and so far have only been able to use SCA drives in the middle of a chain with another, terminated drive. Even in this case, I've only gotten them working on late 90s systems with SCSI, whether internal or external. On both older Macs and Amigas just having one connected locks the system up before it ever starts booting, even when everything about the bus should be correct. As more of my drives die and I have five nice SCA drives sitting on the shelf collecting dust, it's been quite a frustration.

 

[johnklos]

There's only a 2 TB limit. While the SCSI chips support drives larger than 2 TB, the limit comes from using just 32 bits worth of blocks (four billion 512 byte blocks).

SCA isn't a problem so long as you get adapters with high line termination, like so:

https://www.ebay.com/itm/SCA-80-Pin-to-IDC-50-IDC-Male-Adapter-with-High-Line-Termination/233090532398

Likewise, 68 pin SCSI drives with 68 to 50 pin adapters work fine so long as termination is for all 68 pins, like so. The 50 pin motherboard connector has an adapter to go to 68 pin, and the 68 pin drive (SCSI to IDE) and terminator are both 68 pin.

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