Not all HBA adapters are created alike

Moving my backup NAS to a Dell R620, the version I ended up purchasing has three low-profile PCIe slots (riser 1 + riser 3). While I hadn’t spent time considering it, this meant that I could no longer insert my full-height SAS9201-16e adapter into the chassis. I searched for a replacement, and found the SAS9207-8e for a reasonable price.
What I later learned is that I was relying on a feature that the 9207 doesn’t seem to have: redundant SFF-8088 capabilities. When I had installed the 9201, I had run two cables between the adapter and my external JBOD storage (the NetApp DS4243 previously discussed). Doing the same thing with the 9207 results in a lot of conflicts, since instead of detecting that the two cables are connected to the same system, it instead sees two copies of the same system. You can quickly see how FreeNAS would get confused when seeing two copies of the drives, and trying to mount the same drives twice. I had tried updating the 9207 to the latest firmware, but never found a way to enable this same redundancy with this adapter.
So I was stuck using a single cable. Not a big deal, right? Well occasionally I would get communication errors, and once during a lightning storm the single link completely died, resulting in some (minor) data corruption of the JBOD array.
While I can’t guarantee the redundant connection would have saved me in this case, I believe it is a more robust solution. I ended up purchasing a different R620 chassis enclosure (riser 2 + riser 3) and moving the electronics over to this so I can swap back to my 9201-16e. I will continue testing to see if this does in fact improve reliability.
What’s most annoying is that I can’t seem to see this feature listed in either of the product’s documentation. So without trying, it would be hard to know which HBA adapter provides this feature.

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