I have a server with a big hardware RAID6 array that's been configured with two volumes, presented by Linux as
sdb (yeah, I know, but it's a rented colo that came configured this way, and sadly I have to live with it).
I have an I/O-intensive process that uses
sdb. I've run with
ionice -c3, as I want it to take lower priority than anything else. Unfortunately,
ionice doesn't know that the two devices are actually sharing the same array's bandwidth. When that process is busy, the kernel sees that
sdb is quiet and gives it all the bandwidth it needs. However, this can make
sda very slow, because (as I understand it)
ionice works on a per-device basis.
Is there any way of getting the kernel to balance disk I/O across all devices?