arc_write
dr->dr_zio = arc_write(zio, os->os_spa, txg,
zio_nowait(arc_write(pio, os->os_spa, txg,
zio = arc_write(pio, os->os_spa, tx->tx_txg,
zio_t *arc_write(zio_t *pio, spa_t *spa, uint64_t txg,