If you want to build a Linux or FreeBSD system around a RAID array, don’t use the Promise SuperTrak SX6000 controller. At least not for now.
The card used to work under Linux using the standard I2O drivers (i2o_block, etc.), but sometime last year Promise changed the firmware so that it no longer uses I2O. Now you’re stuck with Promise’s own driver, so if you want to use an old enough distribution* (say, Red Hat 7.3) that you can find a driver disk, or make your own driver disk, go ahead…but don’t expect to be able to upgrade it unless you can create a driver disk for the newer distro. This assumes the source code for the driver will work with recent 2.4 kernels—it won’t compile with 2.6. There has been talk of merging the pti_st driver into the kernel (fortunately it’s GPLed), but I can’t find anything more recent than August. Someday it might work again, but not today.
Now, FreeBSD is another matter. It has built-in drivers (pst), the installer will detect it automatically, and even let you install your entire system to it—without warning you that FreeBSD can’t boot from the SX6000. You can boot from another drive and interact with it once the system’s running, but you can’t put your entire system on the RAID array. (This information is not in the installer, not in the hardware notes, not in the driver man page. I only found the one 1½-year-old mailing list post by the driver’s author, and a bunch of “I don’t think it works” comments in other lists and forums.)
I hope this post will save someone a lot of frustration.
*Of the distributions for which Promise has provided driver disks, only one—SuSE 9.0—hasn’t already been retired.