I have a Dell Poweredge R510 with an LSI SAS2008 controller. The SAS controller has eight Western Digital SATA hard drives attached. Currently the R510 is running Debian and can see all eight hard drives. If I boot into the SAS controller's BIOS it can see all eight hard drives. If, however, I boot into FreeBSD 12.2 it only sees seven of the eight hard drives.
Booting back into Linux it gives this information about the SAS controller:
02:00.0 Serial Attached SCSI controller : LSI Logic / Symbios Logic SAS2008 PCI-Express Fusion-MPT SAS-2 [Falcon] [1000:0072] (rev 03)
Subsystem: Dell PERC H200 Integrated [1028:1f1e]
Kernel driver in use: mpt3sas
Kernel modules: mpt3sas
I'm not familiar with BSD so if there's any additional information you need from within FreeBSD let me know.