Disk Percent Busy, out of whack??

Elapsed time: 00:01:00

Pct I/O Rqs Read Wrt Read Write %
Unit Full Rqs Sz(K) Rqs Rqs K K Busy
1 74.9 326.1 38.8 .0 326.1 .0 38.8 48
2 74.9 313.7 40.0 .0 313.7 .0 40.0 2
3 74.9 315.3 40.0 .0 315.3 .0 40.0 2
4 74.9 316.2 40.0 .0 316.2 .0 40.0 2
5 74.9 317.5 39.7 .0 317.5 .0 39.7 2
6 74.9 322.8 39.1 .0 322.8 .0 39.1 2
7 74.9 317.8 39.7 .0 317.8 .0 39.7 2
8 74.9 316.5 39.9 .0 316.5 .0 39.9 2
9 74.9 319.7 39.4 .0 319.7 .0 39.4 2

All above drives are identical. (15K 140G SAS)
All are in the same RAID set.
All contain RAID Stripe data.
Power8, i 7.2, Internal RAID controller.
These drives (and the entire RAID set) are an iASP, so Drive 1 above is NOT the load source.

ONLY job running on these drives is CRTNWSSTG.

So over this one minute how can 1 of the drives be 48 percent busy and the others only 2%? The seemingly insignificant difference in I/Os just doesn't seem like it could possibly cause that large delta in percent busy!