For those asking about the backplane/expander in these supermicro 216 chassis.
HERE is the manual that you want to read carefully.
And this is the picture that explains it all;
As you can see, the SAS2-216EB is a BACKPLANE. Connected to that backplane are the SAS2-216EL DAUGHTER CARD(S). When you purchase a EL1 variant of this chassis it will have a single daughter card. That daughter card has 3 SAS SFF-8087 ports (mini-SAS, iPass, or whatever you call it). But as mentioned further in the manual;
Which says, 2 of those SAS ports provide cascading and failover. That leave the EL1 variants with a single SFF-8087 port for connecting all 24 disks. A single SFF-8087 port will provide 4 "lanes". So for a SAS2 expander that will provide; 4*6Gbps=24Gbps or 4*600MB/s = 2400MB/s. With an SSD pushing 500MB/s, 4 of those are going to be close to saturating the link already.
So the TQ variant will have individual connections for each hard drive (so 24 6Gbps connectors). The A variants will have 6 SFF-8087 connections (4 lanes each) which reduces cable clutter while still covering the type of speed you will see from SAS/SATA SSD disks.
Personally, I wouldn't purchase an EL1 expander variant for anything more the 12 disk chassis (and not all 12 were going to be SSD's). Even the EL2 variant (with 2 daughter cards) only provides 2 SFF-8087 connections (ie. 8 lanes). Which is why at 24 2.5" disks I prefer the A variant.