> One thing I don't understand is why BBU will result in a huge > performance gain. I thought BBU was all about power failures?
Well, it makes it safe for the controller to consider the write complete as soon as it hits the RAM cache, rather than waiting for persistence to the disk itself. It can then schedule the writes in a manner which is efficient based on the physical medium.
Something like this was probably happening on your non-server machines, but without BBU it was not actually safe. Server class machines tend to be more conservative about not losing your data, but without a RAID controller with BBU cache, that slows writes down to the speed of the rotating disks.
-Kevin
Thanks for the explanations that makes things clearer. It still amazes me that it would account for a 5x change in IO.
