SATA/SAS Cascading, with mix of SATA & SAS

[jmoschetti45]

Few questions, I've read a lot about SAS, and I think I got it, but just in case...

Main box: 24 bay supermicro with BPN-SAS2-846EL1 backplane, LSI 9210-8i in IT.
Currently has 2 SFF8087 cables from backplane to HBA, although the book says you only need 1.
Getting filled with SATA3 drives.
Benefits to 2? More lanes for more bandwidth? Redundancy?

External box: CSE-216 CSE-PTJBOD-CB2 with BPN-SAS2-216EB and 2 SAS2-216EL2 expanders.
Has 2 SFF8087 cables from each expander to 2 external SFF8088 ports (so 4 ports total).
Getting filled with SATA3 SSD and spinning rust, probably 50/50.

From what makes sense to me from the SATA days. 1 cable from each "out" port to one of the 2 "in" ports on a second HBA in the main box.

I've seen people run 4, 2 from each to 2 separate HBAs. More bandwidth? Redundancy? (would need dual port sas drives tho???)

Since each of the expanders have 3 ports, could I run 4 cables up to the main box to 2 HBAs for maximum bandwidth, then use the remaining 2 to eventually add a second box downstream with reduced bandwidth? (eg: fill this one with SSD, 2nd box with rust?)

 

[Johnnie Black]

Two cables from one HBA to a single expander doubles the bandwidth, like in you first case, with dual expanders you can also double bandwidth by connecting two cables from the same HBA to one expander, or redundancy by connecting one cable to each expander to the same or a different HBA.

 

[Johnnie Black]

Forgot to mention, AFAIK redundacy only works with dual port SAS devices (multipath), and yes you can cascade to a second box, but single link only, with or without redundancy.

 

[jmoschetti45]

Ok. Thanks. Looks like my best bet is 2 cables from HBA to 1 expander.