Okay, well with that, I guess I better give the very basic gloss over on the Interface cards. This is NOT in depth or all encompassing for the IT pros, just a very basic primer for the non IT types and/or home users. I will aslo tell you here, I have not had a Snap Expansion unit to test with myself, this information mostly comes from documentation, not personal experience, at least in the case of the expansion units. Keep that in mind please, and correct me if you see a mistake, but if you do, be sure the info you put out is 100% correct please.
As I mentioned before, there are 3 different type cards I have seen factory installed in the Guardian Snap Server 4400, 4200, 4500, and 15000. These are SCSI, SATA, and Fibre Optic. Please notice I said factory installed. The 4400 has a single PCI card slot (half height) and the 4200, 4500, 15000 have two full height slots, one being PCI and the other being PCI-X. Pretty much any card of the right card type can be installed in these units since these are standard slots (like a video card or other Interface card and so on). The key is if the OS will have drivers built in for it and have options to utilize the card (if using the Guardian OS). With the Guardian OS, you are pretty much stuck with using the cards that have been factory installed, or cards like a video card and so forth that do not require an OS installed driver or OS supported options for BASIC operation. I used the Video card as the example because it helps with a 4400 that does not have a Video adapter for basic POST use.
In the case of the Guardian OS Snap Servers, these cards are used for external interfacing to other devices, via SCSI, SATA, and Fibre Optics. Some of the cards may have internal connectors, but they are not used for internal unit use in any units I have seen.
What kind of devices am I talking about? Well, how about tape backup units, or expansion units as the main uses? They can be used for MANY MANY other things, but this is the primary uses most often. There are other expansion units, but the main ones for these units are the Snap Disk 10 and Snap Disk 30.
The Snap Disk 10: Is a 4 drive unit that looks very much like a 4200, 4500, or 15000 unit. It contains 4 drives and the interface to connect to one of these units and adds 4 additional drive for those units. I have not used one myself, but the documentation indicates that these additional 4 drives can be mixed in with your current RAID arrays, or as Spares, or as their own RAID arrays with the 4200, 4500, or 15000 acting as the head unit (the actual Server). Thus making your 4 drive unit an 8 drive unit. The only bottleneck will be the speed of the interface being used. This is a very good and cool thing.
The factory installed interface for use with a Snap Disk 10 is a SATA interface (the units both still use PATA drives). This uses a proprietary connector cable and looks just like a SCSI connector. Many people think the Snap Disk 10 is SCSI, but it is actually a SATA connection. In the circles I travel in, I have been told you could replace the interfaces with the SCSI interfaces, for higher speed and reliability, but I do not know if it has been done etc. But, in theory, it should work. However, not having a Snap Disk 10 myself, I cannot say if this can be done in the Snap Disk 10 or not. Maybe David will pipe in here since he has one. The factory installed interface though, is a SCSI looking SATA interface.
The Snap Disk 30: Is my favorite of these devices. I will have one some day!
This unit is similar to a Snap Disk 10, except that it uses a Fibre Optic interface and has 16 Drives! This will turn your 4200, 4500, 15000 unit into a 20 Drive unit for practical application. WOW! I do not know if it could be converted to the SATA or SCSI adapter (since I have not seen the insides of one), but it really doesn't matter. Why? Because the SATA and SCSI interfaces simply would not be able to keep up with the data flow required for arrays with this many drives, not to mention reliability of data bits keeping the arrays intact. Thus why it uses the Fibre Optics Interface. I would also not use less than a full Pentium 4 2.4 Ghz CPU or less than 1 GB of Reg ECC DDR as a minimum. I think 2.6 or 2.8 Ghz and above with 2 GB of Reg ECC DDR is much better. In fact, this is why the Snap 15000 has a 3 Ghz CPU and 2 GB of Reg ECC DDR. The 15000 is designed as the Head Unit for a Snap Disk 30, and also why it comes with a Fibre Optic card.
Now for some prices on these cards. The SCSI cards can be found on average for $200 on eBay and elsewhere, but this IMO is a little high in price. If you look around, and watch eBay, you can find them sometimes for $100 and if you are patient, $75. The SATA cards seem to be harder to find and get confused as SCSI cards quite often. Now the Fibre Optic cards are a different matter. They are expensive! I have yet to see one for sale anywhere, including eBay, for less that $798. I am sure they can be had for less, but you will have to be real resourcefull and very patient, as well as lucky.
Back to the Snap Disk 30 a moment, for those wanting to expand. They are normally in the $1600, $2000, and $2500 zone, but I recently saw a New Open Box Snap Disk 30 on eBay with all 16 x 250 GB drives installed (4TB) for $900. If I had the money at the time, I would have snapped it up (parden the pun). If you are patient, you can get them for these kinds of prices. Just remember, you have to have a Fibre Optic card to use the Snap Disk 30.
DO NOT underestimate the uses for these Interface cards. They can be used for a multitude of things. Even if you do not think you want or need one now, you may very well some day. Thus, when you buy Guardian Snap Servers, watch to see if they have these cards installed or can be upgraded to include them.
I hope this helps...