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
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