On Wed, Jan 11, 2012, Chris Cappuccio wrote: > If only one disk is affected at a time, 5.0 is the fastest, and has the > most trouble with responsiveness while being fast, this is likely to be > improved by a fair I/O scheduler. There is a generic framework in place > now for schedulers to get plugged in I don't think anybody has actually > written it yet. > > There's also an issue with dirty buffers getting eaten up, but that is > prominent on slow devices, and you'd be WAITing in buf_needva in that case.
I don't think needva has been totally ruled out from what I've seen, though it's less likely. My other guess is that the raid card itself prioritizes writes over reads leading to a backlog of read requests.
