SD_UNMAP_MAX_DESCR
descr_cnt_lim = MIN(lim->lim_max_unmap_descr_cnt, SD_UNMAP_MAX_DESCR);
lim->lim_max_unmap_descr_cnt = SD_UNMAP_MAX_DESCR;
SD_UNMAP_MAX_DESCR * sizeof (unmap_blk_descr_t))
