What SATA drive should I install FreeBSD onto? i.e. ar0 vs da0 vs ad4/5

I'm installing FreeBSD 8.0 on a server that has hardware SATA Raid.

I'm just wondering. What is the difference between these devices.

i.e. ar0, da0, ad4, ad5 I take it that ad4 & 5 are my two disks. Somehow the OS can see them individually even though it's one logical mirrored drive.

Should I be installing it onto ar0 or one of the adX disks. What is da0? it's smaller than the others. ar0 is not some kind of software raid device is it?

Just want to make sure I don't mess this up right from the get go.

From serverfault Matt

• It's hard to say without knowing the system configuration (controller type, etc.) but you probably want to install onto the arN device -- see http://www.freebsd.org/doc/en/books/handbook/raid.html (Hardware RAID - about 3/4 of the way down) & the ataraid(4) manpage.

  See also the gmirror(8) manpage & various bits of documentation on using that -- it's a bit more initial work, but I find it better documented than the ataraid stuff...

  Matt : ar0. da0 - the flash disk plugged into the server. ad4/5 the disks. Not sure what would happen if I install on either of those. After all it's hardware raided. Will it still mirror?

  voretaq7 : Most of the SATA RAID stuff is actually software RAID (which is why you're getting an `ar0` device) -- If you have what FreeBSD considers a "real RAID controller" you'd have a different device name. I'm honestly not sure what would happen if you have the SATA RAID option enabled in BIOS and you write directly to one of the underlying `adN` disks but my gut says "bad things", which is why you'd want to write to the `ar0` device (or switch off the BIOS RAID and do it with gmirror or similar :-)

  Andrew : Commonly known as fakeraid - http://en.wikipedia.org/wiki/RAID#Firmware.2Fdriver-based_RAID_.28.22FakeRAID.22.29
  From voretaq7