For those toying with the idea of modding a C6100, here is how the disk subsystem is built and wired:
The path goes like this:
Disk <-> Backplane <--> breakout Cable <--> Midplane board <--> Interposer board <--> Cable <--> Motherboard
That's a fairly complicated path, but the good news is that you can
"intercept" at several different points using standard cables and
connectors.
In more detail:
•The disks are in a hot-swap backplane, either twelve x 3.5" or 24 x 2.5" disks. I'm only going to describe the twelve disk version here. The 24 disk uses a different backplane and midplane.
•The backplane gets power from both power supplies for redundancy. Voltages are standard, but the power connectors are not four-pin Molex.
•The "front side" disk connectors are single-ported SAS/SATA.
•The "back side" disk connectors (on the rear of the backplane) are normal SAS/SATA ports.
•A "forward" breakout cable combines sets of three SAS/SATA connectors to a SFF-8087 SAS connector. There are a total of four of these cables, one for each motherboard, three disks each.
•Each breakout cable plugs into the midplane board. The midplane board has two SFF-8087 connectors for each motherboard - eight total. Normally, only one is used per motherboard.
•The midplane board connects to the interposer board using a large connector. Within the interposer, the disk channels are converted to SATA connectors. While the midplane has two SFF-8087 connectors per motherboard for a total of eight disk channels, only six are converted to SATA - four from one connector and two from the other. The midplane is part of the chassis while the interposer is part of the slide-out motherboard cartridge, so this connection is made or broken when the motherboard chassis is inserted or removed.
•Cables connect the SATA connectors on the interposer board to the connectors on the motherboard. In a standard system these are SATA to SATA cables but if a SAS mezzanine card is in use, then one of them is a SFF-8087 to SATA "forward" breakout cable.
Rephrased:
Backplane: SATA disk in, SATA out.
Breakout cable: SATA in, SFF-8087 out
Midplane: SFF-8087 in, large custom connector out
Interposer: Large custom connector in, SATA out
Motherboard: SATA in
Each motherboard has six disk connectors on its interposer board and so can be wired to up to six disks without losing the ability to hot swap motherboards in and out of the chassis. If you need more than six disks for one motherboard, you can make it work, but you'll have a frankenstein on your hands when you are done.