So along time ago I did a thread about raid and how to and what not... back then I elaborated on the various levels and which is better or safer or faster. Today I will be looking at raid cards and on board raid.
First off all on board raid is fake raid. What is fake raid? Fake raid is basically a host card/chipset with a small bios which offloads processing to OS and CPU. The information about the array is offloaded to the master drive in the array. Sounds cheap well that's the general idea and that's why it works so nice in windows and only windows.
Linux does not recognise and never will recognise fake raid. Whatever array you create linux will see only single disk plain and simple. You could always use the DMRaid topology but that is just not right.
Below is a comprehensive list of some fake raid and real raid cards.
http://linuxmafia.com/faq/Hardware/sata.html
If you running windows alone you are more or less fine... but ponder this. If you change your motherboard and happen to move from say an AMD (SB700/SB750) and migrate to an Intel (ICHr 7/8/9/10) then your beautiful raid 10 data array just got busted. If you had a raid card on the other hand, slot it back in and go.
Other major benefits include dedicated on board cpu such as the infamous XOR from intel (when you think about it guys intel is the best)... they created ethernet as we know today, they created the PCI bus, and many more things. Coming back on track the XOR cpu was immediately adopted by raid card makers world wide. It took care of mathematical stuff in raid levels such as Raid 3/5/6/50 which is to say raid with parity.
Cache memory is also an accompaniment with raid cards and will be with his side man the Battery Backup Unit (BBU) which makes raid even faster for the option write back. The bigger the cache the better the performance it is that simple. Most cards now come with 512MB DDR2 which is more than what some folks have as their main memory.
Real raid cards will do rebuilds online or offline and will not affect data access that much depending on the raid level being reconstructed. Real raid cards will use pci-e x4 and upwards and pci-x 133MHz for true bandwidth. Lastly real raid cards are not cheap.
all content from maxfactors head... feel free to quote