i understand that even though we buy a RAID card off the shelf, it may still be software raid. How do we identify.. what's the characteristic/specifications to a 'software' RAID card?

And while we're on the topic, can anyone advice if running software raid (using linux to manage) will cause the system to be severely slower... as in performance lost (a great deal)?

Software RAID is done without a "card". If you have a card that does RAID then by definition it is hardware RAID.

I recently installed a RHEL 4 server using software RAID (RAID 1 mirroring). Compared to the ones I've done hardware RAID on it formatted the filesystems I laid out much more slowly. Haven't done any performance analysis after that but feel fairly confident software RAID has to be slower than hardware simply because it has to use more OS resources.

Having said that however it is important to know your requirements. If you're running an app that isn't I/O intensive then worrying about the difference between software and hardware RAID may not be necessary. If you're running a large DB (MySQL/Oracle) then you want to maximize disk I/O. Of course I'd always go hardware RAID where available.

yeah i know hardware card... IS hardware raid.

What I understand is that some hardware raid cards, are infact using software to do the raid.. thus am trying to find out more here.