You should be able to get a decent SCSI hard drive for next to nothing. Especially the smaller capacity hard drives. I'd check a couple of things before I give up on the drive though.
Start by making sure that it's not the SCSI cable that is causing you problems. You can do that by trying the drive in another machine. Or, you could simply try a different SCSI cable on your Classic. You might also want to check the SCSI ID setting on your drive to make sure you're not having an ID conflict. Only SCSI ID's 0 through 6 are available for use by devices. Make sure your drive is not set to use ID 7. This is the SCSI ID that your Macintosh computer uses, and will cause conflicts if your drive is configured to use ID 7 as well.
I trust that you've already checked to make sure that the logic board end of the SCSI cable is firmly seated in its 50 pin socket?
Finally, if you determine that the drive is in fact the culprit, I would avoid getting an overly large drive for your Classic. Simple fact of the matter is that a compact Mac with only four megabytes of RAM will not be able to run probably 90% of the Macintosh software that is readily available. So spending a few extra bucks on a drive that will likely never be filled to capacity is probably not worthwhile. You may also have some heat and power issues to contend with if you stuff a large capacity drive in there. Though I'm not entirely certain about that last bit.
Start by making sure that it's not the SCSI cable that is causing you problems. You can do that by trying the drive in another machine. Or, you could simply try a different SCSI cable on your Classic. You might also want to check the SCSI ID setting on your drive to make sure you're not having an ID conflict. Only SCSI ID's 0 through 6 are available for use by devices. Make sure your drive is not set to use ID 7. This is the SCSI ID that your Macintosh computer uses, and will cause conflicts if your drive is configured to use ID 7 as well.
I trust that you've already checked to make sure that the logic board end of the SCSI cable is firmly seated in its 50 pin socket?
Finally, if you determine that the drive is in fact the culprit, I would avoid getting an overly large drive for your Classic. Simple fact of the matter is that a compact Mac with only four megabytes of RAM will not be able to run probably 90% of the Macintosh software that is readily available. So spending a few extra bucks on a drive that will likely never be filled to capacity is probably not worthwhile. You may also have some heat and power issues to contend with if you stuff a large capacity drive in there. Though I'm not entirely certain about that last bit.