With overstriping, lod_check_and_reserve_ost() lets the RR loop reuse
an OST while lag_ost_avail says unique OSTs remain. That count includes
OSTs RR skips, such as inactive or degraded ones, so an EC data
component can reuse an OST before lod_ec_add_data() takes over, which
repeats the placed stripes assuming they are unique and so puts two
stripes of a raid set on one OST, e.g. -C 13 --ec 5+2 on 8 OSTs with
one down.

Leave all OST reuse for EC components to lod_ec_add_data() and
lod_ec_add_parities(), which keep each raid set on distinct OSTs.