Solution 1: Adaptec 2820SA SATA RAID only has 8 SATA ports, thus you could only hook up 8 SATA drives of your 20 slots available. You could not use SAS drives with this RAID board, but you can use SATA drives in this system. You just need two mini-sas to drive break out cables. This would be your least expensive solution, but you will only get up to 8 usable SATA drives. (Note: I forget which dive you can't plug into what connector, but either SAS drives will plug into SATA connectors, but not the other way... the back plane manual should let you know if it supports either/or)
Solution 2: Buy a SAS/SATA RAID card with 5+ mini-sas connectors (20+ ports). There may be a few out there that can support this many. Then you can populate the drive back plane with either SAS or SATA drives. LSI has plenty of options for SAS/SATA options. Note: SAS drives are significantly more expensive, but do have better reliability.
I actually have 3 2820SA cards in the machine, so I should be able to use all 20 bays.
Do you know where these cables are available?
I bought some mini-sas to 4 port SATA cables today, but they didn't seem to work with the backplanes, the drives were not detected, but from a bit of research, I found that there are two types of cables, one which works with Mini-SAS on the host side, and SATA on the target side, and another which does SATA on the host side, and Mini-SAS at the target side. I will search for the SATA (host) to Mini-SAS (target) cables.
Buying a new SAS/SATA RAID card with 5 mini-sas connectors would be way over my budget.
r_manic : Yup. I searched, and only found the Mini-SAS to 4 port SATA cable.
You can try Molex or Amphenol. These are a couple of the biggest connector and cable manufacturers. Molex is the company that came up with the Mini-SAS connectors and cable system. Digikey or Mouser may have cables? maybe? You are correct, most go from mini-sas host to SATA drive. You basically want pass though type cables. I do not know if Adaptec, 3ware, LSI, etc sell cables separately... but if they do, they may have ones that are pass though... then again, this is not the normal configuration.