// returns the occurrence of each buckets in all disks
func listAllBuckets(ctx context.Context, storageDisks []StorageAPI, healBuckets map[string]VolInfo, readQuorum int) error {
	g := errgroup.WithNErrs(len(storageDisks))
	var mu sync.Mutex
	for index := range storageDisks {
		index := index
		g.Go(func() error {
			if storageDisks[index] == nil {
				// we ignore disk not found errors
				return nil