u64max
vol->size = u64max(vol->size, PLEX[vol->plex[i]].length);
vol->size = u64max(plex->length, vol->size);
vol->size = u64max(vol->size, PLEX[vol->plex[i]].length);
VOL[plex->volno].size = u64max(VOL[plex->volno].size, plex->length); /* adjust its size */