Reads for raid1 bdevs are balanced. Algorithm tries to evenly distribute
load by sending read I/O to all base bdevs following round-robin, but
skiping base bdev that processed most data so far.
Signed-off-by: Krzysztof Smolinski <krzysztof.smolinski@intel.com>
Change-Id: I7d85411a6421bd7352031efb562ee95f2c612011