To this person who saw my posting, the hard drive you are talking about is only 1/2" tell or 3/4". It is a scsi 2 hard drive. it is a western digital hard drive 2.1 Gb in size.
What he's advising you to do is get an extra interface that can plug into the SCSI ribbon cable, alongside your existing hard drives, to mount an SD card into, for use as a drive.
You might need a different SCSI ribbon cable with extra connectors, but it should work fine alongside your existing drives - you can have up to 7 devices on a SCSI bus system, be they drives, or scanners, or even printers. Or even controllers plugged into different computers, if you want a very local, pretty local fast file transfer. The last one is really a stop gap measure, but can sometimes work between Amigas, even if they have different kinds of SCSI controllers.
You don't really need to put memory on the GVP 2091 SCSI controller card (or a Commodore A2091 either) if you are running a 68040 - the system should work best if the 68040 has the memory to it. GVP did do 68040 cards with onboard SCSI, and they go a lot faster than either versions of the A2091. They also did A4000 only accelerators, and their cards can fit most types of Amiga that came with a floppy, one way or another.
How wide is the SCSI cables? 50 connections, sort of a good 2-3 inches across is typical for a cable plugged into into a GVP. Although your drives might be connected to a SCSI controller somehow wired to the 68040, but it doesn't sound like it in your case. Most GVP cards are just SCSI controllers. Some are both SCSI and 68040.
The nice thing about SD cards is, you can copy files to them to backup your hard drives. And you can use them AS hard drives, only they use much less power, so you actually save money from using them compared to hard drives, in the long run.
Now, you can't quite swap them SD cards straight out of a SCSI adaptor. But you should be able to hot plug them in OK, to such a connection.
And if you setup the adaptor right, you can plug different cards into the same place, from outside of the machine. Easier on a big box Amiga. But it can be done.
The really nice thing about SD cards is, you can write protect them, just like floppies.
Pain in the ass to setup in the first place, but worth it.
