The mfi(4) driver has had some data corruption problems on “Thunderbird” series RAID controllers.  There’s a newer driver, mrsas(4), that replaces mfi(4) for these controllers and does not have these issues, but switching may mean new drive locations and therefore some work to get booting correctly again.  Sascha Wildner has an extensive writeup about what this entails, and how to switch now if you have that hardware (recommended).