Hi and welcome!
About 5 and 6:
5) I have used several 80 pin SCA drives with my vintage Macs, with great success -- within their expected limits of course. I'm using an inexpensive SCA-to-50pin converter, I assume without termination of the unused byte... but just a few things to consider:
-Up to Ultra-160 SCSI (aka Ultra-3) support for "narrow" (8-bit, as used on the Macs) transfers is mandatory, so any disk will do... however, since Ultra-320 / Ultra-4 that mode became optional: some drives will support it, some won't. I've got a 73 GB HP Ultra-4 drive that does work fine with the Macs (don't recall the exact model, though). The SE/30 SCSI bus won't go over 2 MB/s, anyway -- some "fast" disks may score even lower; but the short access time of a fast disk is always welcome.
-Those disks are most unlikely to be "Apple certified", thus the usual Apple formatting utilities will refuse to work with them. You either need a third-party formatter or a patched Apple utility.
-The choice of formatting utility determines performance, compatibility and stability. I usually work with a patched version of Apple's Drive Setup 1.5, but the installed driver seems to prevent the 020/030 machines to boot from it -- although it mounts fine after booting from elsewhere. On the other hand, the older Apple HD SC setup utility doesn't seem to work with disks larger than 2 GB
-About partition sizes: everything just below 2 GB will be fine with any Mac, any OS version. Depending on the model and OS version, anything over that may or may not mount. Partitions over 4 GB do need "modern" machines and/or OSs. It seems that the mere presence of a single "large" partition will prevent mounting any partition on a '030 with 7.5.5, while the same disk on a '040 on 7.5.3 is at least capable of mounting those below 4 GB. '040 on 7.6.1 did mount all (Standard HFS, of course). Drive Setup won't let you specify more than 8 "user" partitions on a disk.
6) Assuming you have no conflicting SCSI ID's, you may check for termination issues with utilities like SCSI Probe, Gauge Series' SCSI Info and my favourite: Mt. Everything. If the disk doesn't show up or an error is reported, try things like having the terminator on and off, or another cable.
But maybe you're just missing the driver on the SE/30's system folder. Being Apple branded drives, any version of the Apple driver will do. By the way, if a bootable CD (not necessarily with a System version suitable for the SE/30) is in the drive, powered and spinning at the time of power-up, it should load the driver from that CD and any disk will mount fine afterwards, without any extensions installed on the boot device!
Hope this helps,
About 5 and 6:
5) I have used several 80 pin SCA drives with my vintage Macs, with great success -- within their expected limits of course. I'm using an inexpensive SCA-to-50pin converter, I assume without termination of the unused byte... but just a few things to consider:
-Up to Ultra-160 SCSI (aka Ultra-3) support for "narrow" (8-bit, as used on the Macs) transfers is mandatory, so any disk will do... however, since Ultra-320 / Ultra-4 that mode became optional: some drives will support it, some won't. I've got a 73 GB HP Ultra-4 drive that does work fine with the Macs (don't recall the exact model, though). The SE/30 SCSI bus won't go over 2 MB/s, anyway -- some "fast" disks may score even lower; but the short access time of a fast disk is always welcome.
-Those disks are most unlikely to be "Apple certified", thus the usual Apple formatting utilities will refuse to work with them. You either need a third-party formatter or a patched Apple utility.
-The choice of formatting utility determines performance, compatibility and stability. I usually work with a patched version of Apple's Drive Setup 1.5, but the installed driver seems to prevent the 020/030 machines to boot from it -- although it mounts fine after booting from elsewhere. On the other hand, the older Apple HD SC setup utility doesn't seem to work with disks larger than 2 GB
-About partition sizes: everything just below 2 GB will be fine with any Mac, any OS version. Depending on the model and OS version, anything over that may or may not mount. Partitions over 4 GB do need "modern" machines and/or OSs. It seems that the mere presence of a single "large" partition will prevent mounting any partition on a '030 with 7.5.5, while the same disk on a '040 on 7.5.3 is at least capable of mounting those below 4 GB. '040 on 7.6.1 did mount all (Standard HFS, of course). Drive Setup won't let you specify more than 8 "user" partitions on a disk.
6) Assuming you have no conflicting SCSI ID's, you may check for termination issues with utilities like SCSI Probe, Gauge Series' SCSI Info and my favourite: Mt. Everything. If the disk doesn't show up or an error is reported, try things like having the terminator on and off, or another cable.
But maybe you're just missing the driver on the SE/30's system folder. Being Apple branded drives, any version of the Apple driver will do. By the way, if a bootable CD (not necessarily with a System version suitable for the SE/30) is in the drive, powered and spinning at the time of power-up, it should load the driver from that CD and any disk will mount fine afterwards, without any extensions installed on the boot device!
Hope this helps,