Looking at the videos and blog posts, it would appear that the backplane is a SATA only device.
Ref: Our Biggest Design Decision - Direct Wired or Backplane? - 45Drives Blog
The description on the board, according to the picture in KB450416 - Replacing Backplane (HDD) - 45Drives Knowledge Base, the board says “4 x mini SAS to 15 x SATA”.
Can someone please confirm this? Can I swap the plugs about and get 8 x SAS and 7 x SATA?
I have both SATA and SAS drives in mine and it works fine. I ordered one cable that goes to the HBA and the other breaks out into SATA cables going to my MB onboard controller.
So they are wired for the full SAS 12Gb/S?
HI @Bill, The backplane supports both drive types. It mostly depends on what kind of HBA connection you are making from the backplane to the motherboard. If you are only using a SATA HBA, then SAS will not work, and vice versa
If you are only using a SATA HBA, then SAS will not work, and vice versa
So I’ll need 7 SAS drives for the HL15 as only 8 are from the SATA adapters and 7 are connected to the SAS adapter?
If you use a SATA HBA or SATA ports from your MB to feed the backplane then only SATA drives will work.
If you use a SAS HBA or SAS port from your MB to feed the backplane then both SATA AND SAS drives will work.
Thanks, that is exactly what I wanted to know. 
Hi All,
I’m a bit late to the party, but yes, @ZVeguillaCotto is correct.
With that, the fully built HL15 from us would be able to support all 15 SATA drives, or 7 SAS drives and 8 SATA drives.
If you wish to use all SAS drives, you would need to add another SAS controller to the system and have the backplane connect to that instead.
7 SAS drives and 8 SATA drives.
@Hutch-45Drives Am I able to swap the backplane plugs around and get 8 SAS and 7 SATA?
@Bill, Yes you can do that but if you are using our aliasing tools for the HL15 the order of the drives will be the wrong way around but everything else will work
And if you are using your own OS then that won’t batter.
Awesome thanks. I would have thought that having the option for 8 x SAS would have been the default. I was notified today that my prebuilt was shipped today, so I’ll be able to play around with it soon.
Just as a side note. Our backplane design does support SAS drives but it does not have the capability for multipathing to the drives so you will not see much benefit with using SAS over regular SATA drives
I’m not an expert by any means on this, which is why I was asking. So, if I understand you correctly, I can plug in SAS drives that can do 12Gb/S (using multipathing?) but, although the backplane allows plugging in SAS drives, they will still be effectively treated as SATA drives?
So my thoughts about the blog post and the picture from the replacement guide are correct, it is a 4 x SAS to what is effectively (and electrically) a 15 x SATA adapter, although the middle “SAS blocking” tongue isn’t in the backplane sockets.
SAS supports 12Gb/sec interface speed and also multipathing to two controllers. Practically speaking even the Exos 2X18 only does ~550MB/sec sequential speed which is fine with SATA 6Gb/sec.
Edit - here’s a half decent article on the differences: SAS vs SATA | What Is the Difference & Which Is Better? | ESF
The problem is that during the rebuild the probability of hitting another hard error reaches 100% when just 10TB of data is read (a total of 36TB needs to be read for the rebuild). When this happens there is now a double drive failure and the RAID group is down to eight drives
Damn, impressive that things even work at all in our consumer home labs
Just wanted to clarify this point, if ordering Chassis and backplane only, and adding a SAS HBA such as an LSI 9300 16i - would all 15 ports support SAS drives, or is there still a limitation to 7 drives?
The backplane has four SFF-8643 connectors and supports SAS-3 drives in all bays.
The full build only supports half SAS because of the connections on the motherboard that is used for the full build. That motherboard has a single onboard HBA chip, so only would support 8 SAS drives, with the others effectively being SATA. One could get the full build and install a PCIe 8i HBA if they needed all bays to be SAS for the full build.
FYI - I did the cable swaps to get 8 SAS drives in my HL15 Full Build. I documented on this forum including my changes the alias file.