Having a RAID controller that has eight internal SATA3 lanes, you can get 6 Gb/s on all eight drives. What if I connect a 24 port SAS expander to an eight port RAID controller, do I still get max throughput of 8 x 6 Gb/s, or am I able to get 24 x 6 Gb/s, assuming the expander is rated for 6 Gb/s on all ports?
Of course the PCIe bandwidth is going to limit it, as well as the RAID controller but is this right theoritically speaking? PCIe 2.0 x8 has bandwidth of 4000 MB/s and PCIe 3.0 x8 has 7880 MB/s.
As an example, I was thinking of buying LSI MegaRAID 9271-8i for my home server. It has eight internal SATA 6 Gb/s lanes. With that one I am able to connect eight hard drives and they can work on their limits in terms of transfer rates because there is one 6 Gb/s lane for each drive available. But in the future the storage capacity might be too low. I thought I could just add a SAS expander, like Intel RES2SV240. It is a 24 port expander rated for 6 Gb/s per port. So do I get the full potential out of the expander, to have 6 Gb/s connection for all the possible 24 drives? If so, could I buy the 9271-4i (has only four internal SATA ports) and the Intel SAS expander to be able to connect up to 24 hard drives and have them work at their full speed?