On 04/15/2011 06:05 AM, Christopher Chan wrote: > > Woohoo, next we will be seeing md raid6 also giving comparable results > if that is the case. I am not the only person on this list that thinks > cache is king for raid5/6 on hardware raid boards and the using hardware > raid + bbu cache for better performance one of the two reasons why we > don't do md raid5/6. > > That *is* md RAID6. Sorry I didn't make that clear. I don't use anyone's hardware RAID6 right now because I haven't found a board so far that was as fast as using md. I get better performance from even a BBU backed 95X series 3ware board by using it to serve the drives as JBOD and then using md to do the actual raid. > Yeah, you are right - but cache is primarily to buffer the writes for > performance. Why else go through the expense of getting bbu cache? So > what happens when you tweak bonnie a bit? For smaller writes. When writes *do* fit in the cache you get a big bump. As I said: Helps some cases, not all cases. BBU backed cache helps if you have lots of small writes. Not so much if you are writing gigabytes of stuff more sequentially. -- Benjamin Franz