// be achieved and disks have too many inconsistent versions.
func reduceCommonDataDir(dataDirs []string, writeQuorum int) (dataDir string) {
	dataDirsCount := make(map[string]int)
	for _, ddir := range dataDirs {
		dataDirsCount[ddir]++
	}

	maxCnt := 0
	for ddir, count := range dataDirsCount {
		if maxCnt < count {
			maxCnt = count
			dataDir = ddir
		}
	}

	if maxCnt >= writeQuorum {
		return dataDir
	}